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f^HIS is a practical treatise for the beginner, by one 
^m • whose experience of, and immediate contact with, the 
needs of those who are using the camera, in and out of doorsL! 
both for pleasure and profit, especially fits him to help thd 



I.— AppArmttts. II.— In the Field. III.— In the Dark-room. IV.— Printing and Too- 
inff. v.— Portraiture. VI.— Instantaneous Photography. VII.— Plash-Ugfati 
Photography. VIII.— Orthochromatic or Color-seniitive Photography. IX.—; 
Composite Photography. X.— The " Fathers of Photography.*' Appendix- 
Tables, Formulas, etc. 

This Book is now in its 

Fourth Edition 
■?! Fifth Thousand. 

Yon cannot afford to be witbont it. 

For Sale by all Dealers in Photographic Materials, Book 
sellers, etc., or will be sent, post-paid, by mail to any address 

In Paper Covers, on receipt of Fifty Cents. 
In handsome Red Cloth Binding, with Gilt Lettering, One Dollari 










Capt. W. de W. ABNEY, C.B., R.E., F.R.S., Etc., 








Pa 107^9. 

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I. Introduction ... ... ... ... ... 1 

II. The Salts of Iron ... ... ... ... 28 

III. The Salts of Platinum ... ... ... ... 38 

IV. Preparation of Paper for the Hot-bath Process 51 
V. Production of Prints by the Hot-bath Process 70 

VI. Variations in the Hot-bath Process ... 89 

VII. Platinum in the Bath Process ... 101 

VIII. The Cold-bath Process of the Platinotype 

Company ... ... ... ... ... 112 

IX. The Printing-out Process ... ... ... 125 

X, Platinum Toning ... ... ... ... 136 

XI. Direct Enlargements in Platinum Paper ... 142 

XII. Spectrum Sensitiveness, Gradation, and Rapidity 

OF Platinotype ... ... ... ... 150 

Appendix ... ... ... ... ... ... 155 

AMj-'li><^ •.• ... ••* ... ... ... X I X 




In treating the subject of printing with salts of platinum, 
one cannot fail to remark that the methods at present in 
use have nothing in common with the ordinary process of 
silver printing; that is to say, the platinum salt is not 
darkened, fer se, by mere exposure to light, as is the case 
with the chloride or other salts of silver, but requires the 
intervention of some other chemical reagent. 

In reviewing, therefore, the previous experiments that 
have led up to the modem system of platinotype, it will 
be convenient to divide them into three heads, viz. : 1st, 
where the actual platinum salt darkens by exposjii^to 
light ; 2nd, where some agent is added to make the laUnt 
change in the platinum itseU visible ; and 8rd, where ^me 
other salt, capable in itself of deoxidation by light, is first 
used, and will throw down metallic platinum from solutions 
of the salt. 




Platinum salts, 'p&r se^ are but slightly acted on by light. 
An early experimenter on the subject appears to have been 
Sir John Herschel, who gave to the British Association at 
Oxford, in 1832, an account of the action of light on a 
solution of chloride of platinum neutralized with lime- 
water. Such a solution, when exposed to light, clouded, 
and threw down a white, or, with excess of platinum, a 
yellow precipitate. Johannsen obtained the same reaction 
with a solution of soda and baryta water added to the 
platinic chloride (PtOl4). Herschel noticed that it was only 
the violet end of the spectrum that had this reducing 
action ; when the mixture was protected by a solution of 
potassium bichromate or tincture of rose leaves in sulphuric 
acid, no change took place. 

Gehlen found that an ethereal solution of platinic 
chloride, when exposed to light, first turned a yellow colour, 
and eventually threw down metallic platinum in the form 
of a thin film on the sides of the vessel. Dobereiner 
obtained analogous effects by mixtures of platinic chloride 
and solution of sodium tartrate, tartaric acid, formic and 
oxalic acids. He also appears to have used the double 
platinous salt, chloro-platinite of potassium.* 

Robert Hunt made a good many experiments on the 
action of light on the platinum salts ; mixing a solution 
of platinic chloride and cyanate of potassium, he obtained 
a double percyanate of potassium and platinum, and on 

* According to W. H. Harrison {British Journal of Photography^ 1887, 
p. 101), Dobereiner was in the field before Herschel and the oilers. 


brushing this mixture on paper and exposing it to sunshine, 
he found that after a prolonged exposure only a very faint 
image resulted. He noticed that the chemical action took 
place first in the blue ray, then going on through the 
violet, but not extending much beyond the visible spectram. 
He remarked, however, a curious darkening in the yellow 
ray, which, on continued exposure, disappeared, and finally 
resulted in a bleaching effect. 

With platinic chloride (PtOl4) washed on paper, some 
action certainly took place, but it required the action of a 
deoxidizing agent to make it apparent. He made a good 
many experiments with this salt in conjunction with oxalic, 
tartaric, and formic acids, and some of the cyanogen com- 
pounds. The results varied but slightly, but were some- 
what remarkable, as it appeared that sometimes the action 
of the solar rays was to darken, and sometimes to bleach 
the yellow colour of the salt. This, he thought, might have 
been due to the different quantities of the yellow and blue 
rays present during the different exposures. 

He also tried experiments with the other platinic haloid 
salts, at the instigation of Sir John Herschel,but discovered 
nothing remarkable or any difference in behaviour. 

From the above experiments it is evident that the action 
of light does cause a reduction of the platinic haloid salts, 
reducing them first to platinous haloid, and, on further 
exposure, to metallic platinum. The first action of light 
is apparently to bleach the paper, from the fact that the 
yellow platinic chloride is brighter to the visual nerves than 
the pinkish platinous chloride ; but by prolonged exposure 
it becomes black from the deposition of finely divided 


metallic platinom. Pizzighelli and Hiibl found, as was to 
be expected, that the presence of an easily oxidizable 
organic substance hastened this reduction, the blacken- 
ing taking place more quickly when oxalic acid was 

If the platinous salts be used, the result will be the same, 
leaving out, of course, the first step in reduction. These 
salts behave very much the same as the silver salt — that 
is to say, they are capable, according to Pizzighelli, of 
receiving a latent image, invisible at first, but which can 
be brought into evidence by the addition of suitable 
developing agents. 

We have ourselves made some experiments on a printing- 
out process in platinum, employing the double salt formed 
by adding silver nitrate to platinous chloride. (The actual 
salt employed in our case was the chloro-platinite of 
potassium.) The double salt formed is of a yellow colour, 
and is, according to Lang, a chloro-platinite of silver 
(PtCl22AgCl). Under the influence of light it darkens, but 
very slowly, to a pretty full black. The unaltered salt can 
be dissolved out by strong ammonia; the action is, how- 
ever, too slow to have any practical value. 

In conclusion, we may remark that a direct reduction of 
either platinic or platinous salts, ^^ se^ is not practicable 
as a printing process ; we can therefore dismiss this division, 
and proceed to the second, where a developing agent is used 
to reveal or obtain the metallic deposit. 



Hant found that a neutral solution of platiaic chloride 
(PtCl4), mixed with cyanate of potassium, and after ex- 
posure washed with a solution of mercurous nitrate, gave 
a pretty, though delicate, positive picture. It, however, 
subsequently faded even in the dark. 

If paper prepared and exposed in the same way were 
washed over with nitrate of silver, a faint positive image 
was formed ; on re-exposure to light, the hitherto unacted 
on portions blackened, whilst the already reduced portions 
remained light, and a fairly good negative resulted. 

If this paper be washed over with mercurous nitrate first, 
it assumes a yellowish brown tint. Exposed to sunshine, it 
gives a very peculiar picture, which will be either negative 
or positive, according to the depth of colour, which is 
exceedingly capricious, that is produced. The exposed 
portions often pass into a beautiful vermilion colour, which, 
however, fades with some rapidity, leaving the ground of 
the paper a buff or ruddy brown. 

Paper washed with percyanate of potassium and chloride 
of platinum, and then with nitrate of silver, darkens to a 
well-defined lilac tint. If mercuric chloride be added, even 
with an exposure of fifteen minutes no change is apparent, 
but on treating it with strong ammonia a picture of intense 
blackness on an iron-grey ground is at once formed. 

All the above results of Hunt's were, however, found to 
be unstable, and, after being kept in a portfolio some time, 
completely faded. It is worthy of remark, however, that 
although the picture on the platinum paper had disappeared. 


where they were in contact with argentine papers a good 
image, dark on a light ground, had been transferred to these 

It is difficult to know how much of the above results is 
to be ascribed to platinum, and how much to the other 
metals employed. Considering the great stability of metallic 
platinum, it can hardly be allowed that when once formed 
it could easily be reoxidized. That platinum salts, how- 
ever, are capable of development is a known fact. Gehlen, 
as far back as 1834, showed that an ethereal solution of 
platinum, after a short exposure to light, was reduced by 
ferrous sulphate, and later Pizzighelli and Htibl showed 
that paper washed with chloro-platinite of potassium and 
oxalic acid, after a short exposure to light, was reduced by 
the action of a cold solution of ferrous oxalate. But as in 
our first division, the latent image formed by the platinum 
salts does not offer a practical printing method, and we 
now come to our third and somewhat analogous division, 
where the metallic platinum is reduced from its salts by 
the application of some substance which in itself is incapable 
of causing reduction, but gains this property by exposure 
to light. 


It is in this division that we find all the present known 
systems of printing in platinum. The rationale of the process 
lies in the fact that, whereas the salts of platinum are un- 
affected by a per-salt of the heavy metals, they are reduced 
when in contact with a proto-salt, to which may be added 
some other agent, which, incapable itself of reducing the 


platinam, still accelerates or facilitates the reduction of this 
metal. In order that this fact may be practically made nse 
of for photographic purposes, it is evidently necessary that 
a substance be found which can be reduced by the action of 
light from the per to the proto state, in which case the 
future image will be a positive. For this purpose the salts 
of the heavy metals seem particularly fitted, such as iron, 
uranium, or silver. As all know, the chlorides or other salts 
of these metals, on exposure to light, are reduced either to 
some lower oxide or the metal itself ; the parts therefore so 
acted on by light will have the power, if platinum be pre- 
sented to them, of precipitating it from certain of its salts. 

The Use of Silver for forming the Provisional Image. 

Although not the first used, it will perhaps be better to 
treat of the silver salts first, as they still serve as a basis for 
a form of platinum printing. We allude, of course, to 
toning by means of a salt of platinum. De Carranza * has 
the reputation of being the first to describe this method, 
but the process cannot be said to have been very favourably 
received. At the same time, C. Poupat {Lumwre^ Feb., 
1856) used double chloride of platinum and sodium, and for 
albumenized paper the double hyposulphite of platinum and 

Carranza found many imitators, who each proposed 
platinum toning formulas which differed but slightly from 

* Bulleiin 8oc, Franc. Phot, March, 1856 ; and Journal Phot Soc., 
Marcli 21, 1866. 


his own. Baldus (Photographic Notesy June 1, 1857) uses 
neutral chloride of platinum instead of sel d'or for B. Evrard's 
printing process. Haackman * made the remark that prints 
on matt surface paper toned much more readily than those 
on albumenized. He also recorded the fact that generally 
platinum was less active than gold. Wattf states that 
prints so toned do not fade, although exposed continuously 
to light for years. Gwenthlian % made some experiments in 
platinum toning, and records the fact that alkaUne solutions 
gave brown tones, whereas acid ones produced bluish 

Platinum toning, moreover, was somewhat largely used in 
the bumt-in enamel processes. The image is here formed in 
silver suspended in collodion ; this image is toned by platinum 
till the whole of the silver is replaced by platinum. The 
plaque is then fired, the collodion is all vaporized, and the 
black metaUic platinum left burnt in on the porcelain. This 
process is interesting, as it appears to show that the silver 
is completely replaced by the platinum, for if any of the 
former salt were left in the collodion on the plaque, the 
image would bum out of an unpleasant, greenish colour, 
quite destroying the beauty of the enamel. 

In 1864 {Photographic Nms, 1864, p. 184), a Dr. 
Maugham appears to have made some experiments in 
platinum toning, using the ordinary bichloride, but suggested 
at the same time the use of the double salts of platinum and 
the alkaline chlorides. Reference is also made {ibid,^ p. 184) 

♦ Photographic NewSj vol. i., 1859, p. 261. 

t Ibid,, vol. ii., 1869, p. 206. 

X Jbid.y vol. ii. p. 263; also 1859, Jan. 7, p. 214. 


to some prints produced by Captain Sellon, who is stated to 
have experimented with the sodio-chlorides of platinum, 
rhodium, and iridium, but no details are given. 

With these exceptions, however, platinum toning processes 
have never been in favour with photographers. Their 
action is very slow, the results are uncertain, and inferior 
at the best to those obtained by gold. In fact, it is by no 
means an easy matter to obtain good results when the 
ordinary platinic chloride is used. This salt is found under 
many aliases at the dealers', sometimes being called bichloride 
(a relict of the old chemistry), sometimes tetrachloride, and 
sometimes with the safer title of simply chloride of platinum. 
It really appears to be chloro-platinic acid (PtOl4 2HCl 
+,6H20), the real platinic chloride, PtCl4, being insoluble 
in water, according to Pizzighelli. Watt states that when 
pure it is soluble in water, in which we agree with him. It 
is, probably, the presence of the hydrochloric acid that 
renders the action of the salt so variable, and the best way 
of using the salt is first to neutralize the hydrochloric acid, 
and then reacidify with nitric acid. 

In 1889, Mr. Lyonel Clark described a practical toning 
process with platinum, using for this purpose the chloro- 
platinite of potassium. This was described and specimens 
shown at a meeting of the Camera Club. As the process 
will be described fully further on, we will not now allude to 
ifc any further.* 

Soon after this date Mr. Valentine Blanchard brought out 
his platinum process. He has not, however, described his 

♦ Vogel, Jmir., describes {British Journal of Photography, 1887, p. 471) a 
process of toning bromide prints with potassium chloro-platinite and HCl. 


method of working, which he keeps a secret. His process 
does not appear to differ very materially from the ordinary 
form of platinum toning. He prepares a special matt surface 
paper, which appears to be heavily salted and sensitized. 
The image is considerably over-printed, and then toned in 
his special solution. It may be that he uses one of the 
platinous instead of the platinic salts in his process. 

There is another use of platinum, foreign to printing, 
however, but which is somewhat analogous to it, and that is 
the process of intensification by means of platinum. In 
these processes, as in the toning processes, the silver image 
is replaced or increased by platinum. 

Eder and Toth * made a very close set of experiments on 
the action of platinum chloride on negatives produced by 
the wet process and developed with iron, using platinum 
solutions of different strengths and different degrees of 
acidulation. Generally speaking, they found but little 
difference in the results ; 1 in 800 or 1000 is the strength 
they recommend, but a greater or less degree of con- 
centration only quickens or slows the action, the final result 
being the same. With regard to the acidulation, hydrochloric, 
acetic, and nitric acids were tried ; nitric worked the most 
quickly, and acetic the slowest, the proportions being 20 
drops of nitric, or 30 glacial acetic, or 20 hydrochloric 
acids, added to each 500 cubic cent, of platinic chloride 
(1 in 800). Neutral baths gave no advantage, working 
more slowly than the acid ones. Some experiments that we 
have made with other platinum salts appear to confirm the 

♦ Photographische Correspondenz, yol. xii., 1876, p. 237 ; also British 
Journal of Photography f Dec., 1875. 


above results, it being a carious fact that, whatever the 
degree of concentration, the final result was always the same. 

In this process of intensification, the metallic silver is 
converted into chloride at the expense of the platinic chloride, 
which, in its turn, reverts to the metal. In this state, if the 
plate be treated with hypo, the silver chloride is dissolved out, 
and only the platinum left. In order to attain a still greater 
increase of density, Ederand Toth, instead of dissolving out 
the silver, converteci it again into metallic silver by flowing 
over the converted negative a solution of ferrous sulphate. 
This operation they repeated several times, in order to still 
further increase the density, but found that their eflForts 
were circumscribed, as, after two or three applications, the 
platinum black refused to adhere any longer to the image, 
but was washed away. They also tried the possibility of 
combining the platinum and iron into one solution, so as to 
require only one operation ; they succeeded fairly well, but 
the solution would not keep, the ferrous sulphate gradually 
decomposing the platinic chloride. In spite of these 
numerous and interesting experiments, platinum never 
attained any great vogue as an intensifier for wet plates. 

With the advent of gelatine dry plates, Willis also 
proposed a system of platinum intensification. He converted 
the silver image into an oxalate of silver by treating it with 
ferric oxalate ; * he then washed it, and flowed over it a 
solution of chloro-platinite of potassium. The action of this 
is to convert the silver oxalate into chloro-platinite of silver. 

Ag,C,04 + K,PtCl4 = Ag,PtCI, + KjC.O^ 
Silver oiudate Chloro-platinite Chloro-platinite Potassium 

of potassinm of siWer oxalate 

* P?u)tographic NewSy toI. xxTi., 1882, p. 183, 


This silver chloro-platinite is then treated with the ferrous 
oxalate developer, which reduces it and the platinum, or at 
least a portion of this latter, to their respective metals. 
Unfortunately for the value of this process, platinum has 
the property of rendering gelatine completely insoluble and 
impermeable, causing irregularities, so that the process was 
soon dropped. 

The Use of Metals other than Silver. 

Uranium and iron are so closely allied in their action that 
they may be taken together; however, iron has proved to 
be by far the most suitable salt, the uranium per-salt also 
appearing to slightly reduce the noble metals, so that the 
high lights are not easily kept pure. 

The per-salts of iron have been used as photographic 
agents from the very dawn of photography. Even the old 
Niepce writes in a letter to his brother (June 16, 1816), 
that he had tried an alcohoUc solution of ferric chloride, 
but had not succeeded, owing to the rapid deliquescence of 
the mixture. 

The next worker in this line was Eobert Hunt. In his 
first book on photography,* page 37, he mentions some 
experiments with the chlorides of gold and platinum on 
paper treated with an iodide of silver, but did not succeed — 
for causes we can now understand — ^in obtaining any 
tangible results. Doubtless, too, many of the experiments 
we have described under our second heading may almost 
come under the present, especially that with the per-cyanate 

♦ ** Popular Treatise on the Art of Photography." Glasgow, 1841. 


of potassium, which has doubtless reduced itself to the 
proto state, and thus aided in reducing the platinum salt. 
That he knew of the powerful action that proto-oxalate of 
iron exerts on platinum is evident, for he describes some 
experiments he made in this direction, although, from the 
present state of our knowledge, we can see why he failed. 

Whilst on the subject of the iron salts, we may here 
mention the chrysotype of Sir John Herschel,* who used a 
solution of ammonio-citrate of iron, the exposed portions of 
which had the power of instantly reducing gold or silver 
from their salts. Sir John Herschel does not appear to 
have tried this with platinum, or perhaps, what is more 
likely, he did try it and failed, and therefore left no record 
of his labours. After this, platinum, in conjunction with 
iron or uranium as a photographic agent, appears to have 
lain dormant until the advent of collodion gave a fresh 
impetus to the practice of photography. 

The Due de Luynes was the next person. In a com- 
munication to the French Photographic Society, November, 
1859 {Photographic News, vol. iii. p. 259), he describes a 
gold and platmum printing process. He states that his 
experiments were suggested to him by M. Poitevin, who had 
been making some experiments in a printing process by 
means of perchloride of iron and nitrate of uranium ; the 
parts exposed to light were bleached by light, and on treat- 
ing the print with gallic or pyrogallic acid, he obtained a 
positive from a positive, the gallic acid only combining with 
that part of the iron that remained in the more oxidized state. 

Re-discovering Herschers chrysotype the Duke, reasoning 

* London and Edinburgh Phil, Mag., Sept. and Oct., 1840. 

14 pLatinotype. 

that the less oxidized portion of the iron salt (the proto-salt) 
should reduce gold from its salts, added chloride of gold to 
the above mixture, and obtained, after some considerable 
exposure, a positive brown image from his negative. To 
verify the fact that it was the gold' that formed the image, 
he exposed paper prepared according to Poitevin's direction 
to light, and then passed it through the chloride of gold 
bath, thus absolutely repeating Herschel's experiment with 
the same result. 

Finding, however, that this process did not give him full 

enough intensity in the high lights, he added chloride of 

platinum to the iron solution in the paper ; this was done 

empirically, since it was not then believed that the proto- 

salts of iron would reduce the perchloride of platinum. He 

says that the results, however, were very fine, giving 

Vigorous iron-grey and black prints when, »after exposure, 

*tey were passed through the chloride of gold bath. We 

should remark here, however, that it was not the iron that 

i-educed the platinum ; in fact, as the Duke states, the 

P^iiit, after coming out of the printmg-frame, showed 

^^V a bleached image on a yellow ground ; the most 

probable cause of the reduction was the gold solution. We 

1^ .^®* ^ some experiments, mixed some chloride of 

t^^^ *^® chloro-platinite of potassium, when instantly 

b hi '^^'^^^P-^*^^e> either of metallic gold or platinum, or 

of ffold^ *^p^t. Was thrown down. Now, although terchloride 

tlie latte ^^* throw down perchloride of platinum, yet 

' platinous i^ ^^ ^ ^^^ Duke's prints already reduced to a 

would hav wL^ ^hich case, as our experiments show, it 

"^^n thrown down in the metallic state. 


The fact that the proto-salts of iron alone do not reduce 
platmic salts (or platinous salt, for the matter of that) is 
shown by an experiment of Mr. Willis's, at the 1888 Con- 
ference of the Camera Club.* He took three test-tubes 
containing a solution of proto-salt of iron, and added 
chloride of silver to one, chloride of gold to another, and 
chloride of platinum to the third. Whereas in the first two 
the metals were instantly thrown down, in the third the 
solution remained unchanged. We have further repeated 
the same experiment with paper washed with potassio ferric 
oxalate ; whilst chloride of gold was instantly reduced 
by the exposed portions of such paper, the platinic and 
platinous salts both remained practically unchanged. 

From this it will at once be understood why the earlier 
experiments with platinum failed. According to Van 
Monckhoven, Niepce de St. Victor t also experimented 
exactly the same way as the Due de Luynes. He is said to 
have exposed a piece of paper coated with uranium nitrate, 
and developed the scarcely visible uranous image with 
solutions of gold or platinum. But we should be inclined 
to doubt very much the fact that he obtained images by 
using platinum alone. Bollman also used platinum salts in 
the production of uranium images by applying a mixture of 
uranium and platinum to the paper, and developing or 
intensifying with gold ; the reader will understand the 
reasons of the success of this process. He also first 

* Comsra Clvh JwnmaXy March, 1888. 

t St. Victor was earlier than De Luynes. He descrihed his process 
at the Academic des Sciences, April 12, 1859 (see Photographic News, 
June, 1859, p. 147) ; also ibid,, Dec. 2, 1859, pp. 147 & 149. 


converted the uranous image, into metallic silver, and then 
toned hy means of platinum. This process was also 
described by Krone {BvlL Soc. Franc.^ 1882, April), but 
both these processes are so similar to the Due de Luynes' 
that the inventors can claim but little merit for them. 

Merget, in 1873, was the next worker with platinum 
salts ; he used a solution of platinum chloride mixed with 
one of ferric chloride and tartaric acid. The deliquescent 
ferrous salt formed, in conjunction with mercurial vapour, 
was said to complete the reduction of the platinum. This 
would doubtless be so, the mercury acting in a similar way 
to the gold, being first reduced itself, and then reducing the 
platinum. Besides mercury, Merget tried exposure to hydro- 
gen, sulphuretted hydrogen, and the vapour of iodine. In 
his opinion the conditions of success in working this method 
depend not only on the more or less appropriate choice of 
sensitive substances, but also on the proper preparation and 
physical properties of the sensitive films. When prints are 
produced by the direct or indirect reduction of the salts of 
the precious metals, the vigour of tone produced depends, 
according to Merget, materially on the grain of the 
sensitive film. This may be obtained by the happy selection 
of the proper kind of paper, or by the addition of certain 
substances which, though in a state of fine crystals or 
powder, are yet insoluble, so that their particles nestle in 
between those of the sensitive substance. This process for 
the indirect production of the platinum image? as described 
by Merget, never seems to have got beyond the experimental 
In the same year as Merget described '^^ ^^^ 


experiments, Mr. WUlis brought out and patented his first 
platinotype patent (specification No. 2011, June 5, 1873). 

Dr. van Monckhoven, in a letter to the Bulletin Beige 
(trans. Photographic News, 1880, p. 75), alludes to the 
researches of St. Victor, and says that he (Van Monckhoven) 
had before that date described in the old Btdletin Beige of 
1868 a platinum process, in which he used oxalate of iron 
and ammonia, and developed the image with chloride of 
platinum, gold, or palladium. He states that these prints 
were found to fade. His claim to originality cannot, how- 
ever, be admitted (see British Journal of Photography^ 
1887, p. 55), and his process is of no practical value. 

Mr. Willis, in a paper delivered at the Camera Club 
Conference, 1888 {Camera Club Journal, 1888, vol. ii. p. 49), 
states that, whilst experimenting with the reduction of 
metals by means of the ferrous salts, and especially the 
ferrous oxalate, he was struck with the obstinate way in 
which the platinum salt refused to be thrown down ; he 
came to the conclusion, however, that some chemical could 
be found that would aid this reduction, but for a long time 
his efforts were unsuccessful, tiU a note by a French chemist 
led him to try the neutral oxalate of potash. Considering 
the remarkable action that oxalic acid has in reducing the 
salts of gold, it was to be expected that he was working in 
the right dh*ection. Experiment proved his surmises to be 
correct, for on adding the neutral oxalate to the ferrous 
oxalate, and then adding the platinum chloride, metallic 
platinum was instantly thrown down. 

On this he based his first patent process, in which a 
solution of a salt of platinum, iridium, or gold, or a mixture 



of these, is applied to the surface of paper, wood, or some 
other suitable material, and dried ; it is then coated with 
ferric oxalate or tartrate, again dried, and exposed to light 
under a negative ; a faint brown image will appear, which, 
after being brushed over with a solution of potassium 
oxalate, turns a strong, intense black. 

The following instructions were given by Willis : — 1. Coat 
a piece of paper with a solution of 1 part chloro-platinite of 
potassium in 48 parts of water. When it has been dried, 
dip the paper in a solution of 1 part nitrate of lead in 48 parts 
of water. Dry once more, and brush over with a solution 
of 1 part ferric oxalate in 8 parts of water, to which, in 
order to render the oxalate more soluble, a little oxalic acid 
has been added. After again drying, the paper may be 
exposed under a negative, and then put to float on a hot 
solution of potassium oxalate. Finally, it must be washed 
in a weak solution of oxalic acid in water, then in sodium 
hyposulphite, and lastly again in water. 

2. Proceed as in the previous case, only substituting for 
the lead solution one of 1 part silver nitrate in 60 parts of 
water. When the prints are taken up from the weak 
solution of oxalic acid, they must be dipped either in a 
strong solution of ammonium chloride, or in a weak solution 
of the same salt, and then in a weak one of ammonia. 
Finally, rinse well in water. 

3. The paper is first dipped in a solution of 1 part 
platinic bromide in 40 parts water, then dried, then again 
dipped in a strong solution of ferric taitrate, and afterwards 
once more dried. It is now exposed beneath a negative, 
and the image thus obtained is developed by floating on a 


hot solution of potassium oxalate. Afterwards it is immersed 
in a weak solution of oxalic acid, finally rinsed in water, 
and dried. 

Mr. Willis also introduced a new departure in using a 
platinous instead of a platinic salt from which to form his 
visible image. He says that after his discovery of the 
action of the oxalate of potash, he immediately tried the 
experiment of coating paper with ferric oxalate, and develop- 
ing with the oxalate of potash and chloride of platinum, but 
the experiment was a failure, as he only got a slight 
reduction in the deepest shadows. It then occurred to him 
that a platinous salt — ^that is, one containing two atoms less 
of chlorine — should be more easily reduced, as the ferrous 
salt would have less work to do in splitting up the more 
unstable molecule, and, moreover, less of it would be required. 

Mr. Willis states (Camera Club Journal, vol. ii. p. 48) 
that at that time (1873) he was aware of, or had discovered, 
the following facts : — 

1. Ferric oxalate as a sensitizing agent on which the 
light acts. 

2. Salts of platinous chloride, from which the pigment 
platinum black was to be obtained. 

3. Potassium oxalate, which conveniently may be termed 
the developing agent. 

4. Salts of lead or mercury as aids to reduction. 

The 1873 process, however, was soon found by Mr. Willis 
to be somewhat complicated and not very certain in its 
results, and in 1878 he obtained a new patent (No. 2800, 
July 12, 1878). The chief point in this new process was 
the entire elimination of the silver salt, and, of course, the 


hypoBulpliite bath. He also made a new departure in 
adding cUoro-platinite to the developing bath, as well as the 
surface of the paper. The following is a description of this 

process : — 

Paper or any other suitable support is dipped in a solntion 


Water ... -.• 30 parts. 

Chloro-platinite of potassium ... 1 part. 

Ferric oxalate ... ... ... 4*5 x^rts. 

Lead chloride ... 0'13 part. 

After being dried, the paper is exposed under a negative, 
and the image is brought out by floating on, or dipping in, 
a hot solution of — 

Water ... ... ... ... 30 parts. 

Potassium chloro-platinite 0*5 part. 

Potassium oxalate ... ... ... 8 parts. 

The print is then passed through a weak bath of oxalic 
acid, then washed and dried. 

Willis states also in this specification that in place of the 

chloro-platinite of potassium he can use other salts of this 

metal, or the nobler metals— gold, palladium, and iridium— 

either in the sensitizing mixture or in the developer, 

although he prefers the former salt. He also mentions the 

possibiJifcjr of using or substituting bichloride of mercury for 

chloride of lead. 

Even this process does not appear to have contented Mr. 
Wilhs, for m 1880 he again appUed for and obtained a 
iTTssor ''"''"'""'' " Platinotype (Ko. 1117, March 


This patent is substantially the process now in general 
use, and known as the hot-bath process, and which will be 
fully described in its proper place. We shall, therefore, not 
allude to it any further here, beyond saying that the 
alteration or novelty consisted in applying the requisite 
amount of the platinum salt to the paper itself, and leaving 
it out of the developer altogether ; the lead and silver salts 
in the sensitizing mixture were also abolished. By this 
means the process was simpUfied, and the danger of dis- 
coloration from the use of the lead and silver salts avoided. 

This process, although but little taken up at first, gradually 
grew in the public favour, and at the present time a glance 
at any of the photographic exhibitions shows that the process 
is most largely used by both amateurs and professionals. 

In the exhibition of the Photographic Society in 1880, 
only 15 examples out of 373 are described as being platinum 
prints — ^we except some few specimens sent by the Platino- 
type Company — whereas in 1894 there were 175 out of the 
382 on the walls {British Journal of Photography^ 1894, 
p. 613). 

Another process of platinotype printing is due to Captain 
Pizzighelli, Benjaluka, Bosnia, and was first described by him 
in the Fhotographische Gorrespondmz of October, 1887, and 
January, 1888. In this system Pizzighelli does away with 
the separate developing solution altogether, this being applied 
to the paper itself, by which means, as the ferric salt in the 
paper is gradually reduced by light to the ferrous state, it and 
the oxalate of soda in the paper react on the platinum salt, 
and the metal is produced during the exposure. This reduc- 
tion, however, depends on the presence of moisture in the 


air, and, therefore, in dry weather glycerine or some hygro- 
scopic substance has to be added to it. On removal from 
the printing-frame, the prints require to be merely soaked in 
weak hydrochloric acid to dissolve out the iron salts, and 
after a short washing they are completed. Papers prepared 
according to PizzigheUi*s formula are now obtainable from 
dealers, and as the process is a commercial one, we shall 
again refer to it in its proper place. 

In 1888, Willis again appears with a new platinum 
process, which he first described at the Conference of the 
Camera Club, March 18, 1888 (vide Camera Club Journal^ 
No. xvii. p. 47 ; also No. xix. p. 99 ; and No. xx. p. 103). 
This process, which was called the cold-bath process (not 
to be confounded with the cold-development process of 
1892), did away with platinum in the sensitizing mixture, 
this salt being added to the developer instead. Paper for 
this process is not now in the market, but the prints 
produced by it were of great beauty. It is perhaps 
remarkable for being the iirst platinum process that gave 
rich brown blacks as distinguished from the yellow browns 
given by the sepia process. It could also be worked with 
the paper damped, the colour, indeed, being thereby much 
improved. The preparation of the paper appears to be a 
little uncertain, and with the advent of the 1892 cold- 
development process, which also permitted the obtention of 
rich tones, its manufacture was graduaUy dropped. The 
idea of this process was the saving of the costly platinum 
salt ; but, unfortunately, the developing baths to which the 
platinum was added would not keep, the metal being 
precipitated therefrom after a time, and so the bath soon 


became useless. Unless, therefore, large batches of prints 
were treated at a time, it became really a more expensive 
process, and did not make the way it merited. The real 
cause, however, of the dropping of this brand of paper by 
the Company, is undoubtedly to be found in the fact that 
the 1892 process offered most of the advantages of the 
former one without its drawbacks, whilst being more easily 
manipulated, it was commercially better. 

This latest process, which holds the field, together with the 
old hot-bath process, at the present day, was also first 
described by Willis at the Camera Club in the Conference of 
March 22, 1892 (see Camera Club Journal^ No. Ixix. p. 53 ; 
and No. Ixxii. p. 19). As this process together with the hot- 
bath are the processes in ordinary use at the present time, 
they will be fully described under their respective headings, 
and we will only say here that the improvements in the 
process consist in the fact that the developing solution 
is used at the ordinary temperature of the room, and 
that the development can be retarded to such an extent 
that considerable local manipulations of the print are 
possible. The bubbles and watermarks that so frequently 
spoilt hot-bath prints are in this process entirely avoided, 
as, if on the first application of the developer the prints 
are covered with bubbles, they entirely disappear on a 
second application. Like the platinum in the bath process, 
prints can be developed and printed in a damp state, and in 
addition the paper, according to the inventor, improves by 
keeping, at least up to a certain extent, gaining not only 
greater insolubility, but improving the value of the blacks. 


The Researches of Burnett. 

We have kept the researches of 0. J. Burnett of Edinburgh 
distinct from other early experimenters, because of their varied 
nature and, from a chronological point of view, their im- 
portance. According to the numerous papers of this gentle- 
man, that are to be found in Fhotographic NoteSy Journal of 
the Photographic Society^ Liverpool and Manchester Journal, 
and Photographic News, between the years 1857 and 1859, 
the amount of experiments made are extremely numerous, 
and embrace an examination of most of the salts known to 
be affected by light. But the only ones that interest us are 
those containing results obtained by means of platinum and 
the metals of that group. The first mention that we find of 
this gentleman's work is a record in Sutton's *' Photographic 
Notes" of a paper read before the Photographic Society of 
Scotland on February 10, 1857 (Photographic Notes, vol. ii. 
pp. 97, 160 & 181). Burnett states that this paper was 
delivered before a meeting of the British Association held 
at Edinburgh in 1855, and the specimens referred to were 
shown at that meeting, the paper, however, not being pub- 
lished in the proceedings of the British Association. The 
basis of the processes described and shown was an uranium 
salt, preferably the tartrate, the proofs being developed with 
silver, gold, and platinum (the latter salt being queried in the 
article). In the same paper, however, he states that he had 
experimented in the direction of toning ammonio-nitrate of 
silver paper with platinum, palladium, and rhodium, but with- 
out decided success. In vol. v. p. 88 of the Journal of the 
Photographic Society, Burnett describes prints, exhibited by 
him at the Exhibition at Suffolk Street, in the January of 


that year, and states that they were the same as those shown 
at Edinburgh and at the British Association. He describes 
them as prints in uranium, developed with nitrate of silver, 
and toned with gold, platinum, and palladium. Other prints 
were shown, produced on albumenized paper sensitized with 
ferric nitrate, and developed with silver, and toned with 
platinum. He also showed prints on uranium nitrate 
paper, toned (? developed) with platinum. In a subsequent 
paper {Journal of the Fhotographic Society^ vol. v. p. 228), 
Burnett reconmiends toning, firstly, with the nitrate, sulphate, 
or acetate of platinum ; secondly, with a platinum toning 
bath rendered alkaline by the addition of any alkali or its 
carbonate, or by dissolving hydrated platinic oxide in a 
solution of one of the alkalies or their carbonates; and 
thirdly, neutral or alkaline baths prepared with platinous 
oxide or its salts. In the same article he gives a formula 
for an nrano-nitrate paper, developed with nitrate of silver 
and toned with bichloride of platinum, to which has been 
added a solution of tartrate, acetate, or formiate of potash, 
until the precipitate first formed is redissolved, the solu- 
tion being neutralized with carbonate of ammonia. In 
the Liverpool and Manchester Journal of May 15, 1858, 
Burnett proposed to prepare paper, either plain or collo- 
dionized or gelatinized, with ammonio-ferric oxalate, and 
develop it with gold or palladium, or develop with silver 
and tone with platinum, gold, or palladium, fixing with 
ammonia or oxalate of ammonia. 

In the Fhotographic Journal of July 1, 1859, in a long 
paper on sensitizing and toning baths, Burnett describes 
the following toning baths : — 


1. Bichloride of platinum and carbonate of soda. 

2. Platinum sulphate or nitrate. 

3. The same, with a deoxidizer to reduce the plantinic to 
platinous salts. 

4 and 5 same as 2 and 3, but with platinous sulphate or 

, Burnett here notes that the platinous salts are more 
easily reduced than the platinic ones. 

Further on in the same article he describes toning baths 
with the chloride and nitrate of platinum, and recommends 
the use of the double salts that gold or platinum form with 
chloride of sodium, and says that the chloro-platinite of 
sodium should be tried. He also mentions the chloro-palla- 
dite of sodium as being a capital toning bath. 

It is difficult to know exactly what merit is to be assigned 
to Burnett ; his papers are very numerous, and it is not 
easy to distinguish actual experiments from mere sugges- 
tions. However, it is quite evident that in 1857 he had 
endeavoured to tone silver prints with platinum, and showed 
prints so toned in 1855. This fact gives him priority over 
Carranza, although his paper, not having been published 
until 1857, somewhat militates against this claim. Anyway, 
his uranium experiments, developed with platinum, taking 
the date at 1859, when they were published, although they 
are stated to have been produced in 1857, and shown in the 
same year, gives him priority over De Luynes and St. Victor. 
With regard to this last-named gentleman's supposed dis- 
coveries with uranium salts, Burnett carried on a very 
acrimonious correspondence in the different journals. Lastly, 
as the proposer of, if he did not actually use, the platinous 


salts, both for silver toning and developing prints in uranium, 
Burnett merits considerable kudos. It is, indeed, remarkable 
how near he came to discovering a really practical platinum 
process, namely, the Willis' platinum in the bath process. 
Burnett used ammonio-ferric oxalate, and fixed with am- 
monio oxalate ; and he knew that platinum salts acted as 
developers of paper so prepared. If only, instead of 
wandering oflf into experiments with nearly every known 
and unknown salt, he had stuck to and perfected this 
one process, it cannot be doubted but that the present 
platinotype process must have been forestalled by many 



It will now be abundantly clear from the above historical 
resumi that the most practical results in platinotype are 
obtained by the use of iron as the chemical of which the 
provisional image is formed, and is replaced by the platinum 
according to a true chemical substitution process. We shall 
therefore proceed to examine the behaviour of the different 
salts of iron under the influence of light, borrowing largely 
for this purpose from the careful series of experiments that 
were made on this metal by Dr. Eder.* 

It is known to chemists that all the ferric salts, in the 
presence of organic bodies, are more or less sensitive to 
light, being reduced to the corresponding ferrous stage ; now 
the organic substance would of course be found in the paper 
itself, or in the different sizes, starch, dextrine, gelatine, etc., 
with which the cellulose fibre has been strengthened. 

But, in choosing the most suitable salt, many conditions 
should as far as possible be fulfilled ; first, we naturally seek 

* <' Recent Inyestigations on the Senflitiveness of the Salts of Iron'* 
{PhotographUohe CarretpondenZf toL xyii. p. 219). 



the mixture which is most quickly acted on by light ; secondly, 
the reduction of the ferric salt must not form any substance 
in the paper that would be deleterious to the platinum ; 
thirdly, the salt must be more or less non-crystallizable — 
that is to say, it must be capable of being applied to paper 
in some form that will not crystallize and break up the 
surface in the way that nitrate of silver on a wet collodion 
plate, if allowed to dry, would do. Minor properties which 
are desirable are that some sort of a visible image should be 
formed on the paper to guide the printer as to the state of 
his print. 

Dr. Eder experimented with the following of the ferric 
salts, and determined their rapidity of decomposition by light 
by measuring the amount of ferrous salt that was precipitated 
from their aqueous solutions in a given time. The solutions 
contained from one to five per cent, of ferric chloride, or a 
like equivalent of the particular ferric salt used, the tem- 
perature of the solutions being from 17° to 20° C. 

Ferric chloride and oxalic acid 

... 100 

Ferric oxalate 

... 89 

Ammonio ferric oxalate 

... 80 

Ferric tartrate 

... 80 

Ammonio ferric tartrate 

... 80 

Potassio ferric oxalate 

... 78 

Ammonio ferric citrate 

... 15 

Ferric chloride and citric acid 

... 19 

,. ,, and tartaric acid 

... 25 

tB^kierally speaking, sensitiveness increases with temperature 
and the degree of concentration, at the same time that the 


be qn&nbities of f errooB salt precipitated from 
come BmaUer. 

tBOQ he tried a fresh aet of experiments, for 
[bmes, when dried into paper, might behave 
blyfrom the aqueous Bolutions under the ia- 
it. His method waa to assimilate more closely 
L he likely to obtain when the salts were osed as 
oeitive piocesa — that is to say, when spread and 
ar. He therefore soaked pieces of paper in the 
i exposed them when dry under one of Vogel's 
neters, Bimnltaneoasly, and for au equal lime, 
were then developed with ferricyanide, when, by 
Lhe amount of Tambnll's hlae precipitated, he 
ximpare their senBitiveness. Practically no great 
ras found from the results of the aqueous soln- 

fenic chloride and oxalic acid was the most 
the ferric oxalate was less so ; then follow the 
and sodio-ferric oxttlates, and the potaasio-ferric 
1 the least. The differences in senrntiveness be- 
donble salts alone were not so great as in the 
! aqueous Bolutions, the sodium and ammoniom 
ally being almost equally sensitive. 
i>na& of the redaction of these salts Dr. Eder 

the fact that with the formation of the corre- 
irroua salt carbonic acid is liberated. Dbbereiner 
-'s Jomnal, vol. btii. p. 90) first observed this 
ion of aqueons ferric Bolutions by light in 1831 5 
Suckrow ((?rt the Chemical Action of Light, 1832, 
aper (Dingle's Polytechnic Journal, vol. cilyi. 
d Keynolds (.BritUh Journal of Photography, 


1861, p. 9). The reaction was the most regular in the case 
of the oxalate^ as the quantity of carbonic acid given off 
agrees very closely with that determined theoretically ; it is 
not so regular in the case of the citrate and tartrate, since 
in addition to carbonic acid, acetic and oxalic acids are also 

Of all the above salts of iron examined by Dr. Eder, the 
most sensitive — that is, the mixture of ferric chloride and 
oxalic acid — is not serviceable in platinum printing, as in its 
decomposition by light hydrochloric acid is formed, and this 
is deleterious to the reduction of the platmum salt, and would 
prevent the development of the image. 

Hubl and Pizzighelli made a further series of experiments 
on the oxalates, citrates, and tartrate, with special reference 
to their use in platinotype. Solutions of these salts, the 
degree of concentration being so arranged that after ex- 
posure there might be one molecule of platinous chloride to 
every two molecules of the ferrous salt, were mixed with 
chloro-platinite of potassium, and then applied to paper. 
Strips of such prepared paper were, when dry, exposed under 
a paper actinometer scale simultaneously for an equal time. 

They were then developed with a hot solution of potas- 
sium oxalate ; the result was that the paper prepared with 
ferric oxalate gave a much more intense black deposit, and, 
moreover, its sensitiveness was greater than the slips pre- 
pared with the tartrate and citrate. Further experiments 
with the acetate and formiate proved that the former is 
very little sensitive, and that the latter causes the reduction 
of the platinum salt very rapidly, and even without ex- 
posure to light. 


As the doable salts of the ferric oxalate possess the 
advantage of being procnrable in a crystalline form, a 
property wanting in the simple ferric oxalate, Hiibl and 
Pizzighelli considered it important to submit these salts to 
a similar examination. They could not well employ the 
potassium salt on account of its insufficient solubility in 
water, but the sodium and ammonium salts— of whose 
composition, especially of the amount of water of crystal- 
lization contained in them. Dr. Eder's recent investigations 
had given them complete information— were experimented 
on by these workers. They found, however, that paper so 
prepared was only slightly sensitive, and the images 
obtained inferior as regards intensity or depth of shadow, 
and could not compare with the results obtained by the 
simple ferric oxalate. They explained the unsuccess of 
their trials on the hypothesis that the complete reduction 
of the double salts under exposure is not effected with the 
same readiness and regularity as in the case of simple ferric 
oxalate; they therefore endeavoured to rectify this by 
reducing the quantity of the double salt in the sensitizing 
solution by one-half, and making up the requisite amount 
of iron by the addition of neutral ferric chloride. 

But even with this combination they were unable to 
obtain reactions of any great value ; the intensity of the 
blacks was somewhat improved, but the sensitiveness was 
decreased, and the prints had an unpleasant yellowy-brown 

The upshot of the above experiments was that Pizzighelli 
and Hiibl arrived at the conclusion that the simple 
ferric oxalate — the salt originally used by Willis — was 


the most suitable for the formation of the provisional 

Ferric oxalate is produced by dissolving ferric hydrate 
in oxalic acid, by which means a greeny-brown syrup is 
obtained ; on evaporation a brown syrup is formed, which 
is incapable of crystallization. 

Protected from light, and at temperatures of from 15° 
to 30° C, this solution will keep for months without altera- 
tion.* When heated, however, to 50° 0. for several hours, 
a gradual reduction to the ferrous oxalate takes place, and 
this reduction will be effected much more quickly if the 
solution or paper coated with it is exposed to the action 
of light. The ferrous oxalate thus formed consists of a 
light yellow crystalline powder, soluble with difficulty 
(1 part in 1000 HgO at 15° C), but which is stable under 
the action of light or air, even when in a moist condition. 

Dr. Eder found that this salt, when moistened with 
solutions of the alkaline oxalate, had a very powerful 
reducing action, and, according to Pizzighelli, solutions of 
the alkaline acetates, benzoates, succinates, borates, and 
phosphates, as well as the solutions of the alkalis and of 
the alkaUne carbonates, produced the same effect. They 
ascribe the reaction to the formation of either soluble 
double salts, or insoluble ferrous salts, having energetic 
reducing effects. With the caustic alkalis, and especially 
with the alkaline carbonates, ferrous oxide itself is probably 
formed, a well-known reduction agent. 

* Dr. Eder and E. Valenta, ** On the Iron Oxalates and some of their 
Double Salts." ** Transactions Imperial Academy of Science at Vienna,*' 
Part II., October, 1880. 



The Action of the Spbctbum on the Salts of Iron. 

Dr. Eder, to whom we are largely indebted already for his 
researches on the behaviour of the iron salts under the 
action of light, has also published an interesting acconnt 
of their behaviour in different parts of the spectrum.* 

From these experiments we cull the following results, 
which may be found useful in examining the general 
behaviour of platinotype processes. 

Febrous Salts. 

Ferrous, as well as ferric salts, are reducible both by light 
and heat. In the dark, however, ferrous sulphate oxidizes 
less rapidly than when in contact with air and red light, 
and the purely chemical action, when shaded from light, is 
greater than oxidation in presence of violet light. 

According to Chastang the oxidation is as follows : — 

In darkness I'OO 

Red light ... ... ••• ••• ... 1*46 

Violet light ... ... ... .... ... '31 

Green light ... .. ... '80 

The oxide formed was ascertained volumetrically. 

Feebic Salts. 
A solution of ferric chloride in ether passes into the 
ferrous state when exposed behind blue or white glass, and 
not behind yellow or red (A. Vogel). According to Chas- 
tang the violet rays are those which reduce solutions of 
ferric chloride in ether to the ferrous chloride with the 

* " The Chemical Effect of the Spectrum," by Dr. J. Eder, trans, by 
Capt. W. de W. Abney (Harrison and Sons: London, 59, PaU Mall, 1883). 


greatest rapidity. In the dark or in yellow or red light 
a little ferric oxide separates. Dobereiner found that an 
aqueous solution of ferric oxalate was decomposed into 
carbonic acid and ferrous oxalate by sunlight and by blue 
and violet Ught, but not by red or yellow {Schweigger*8 
Joumaly vol. Ixii. p. 92). 

Suckow found that the action of light on ferric oxalate, 
after passing through a violet glass, was the same as that 
of white light; the action was retarded by a blue glass, 
and still more by a green. In yellow or red light he 
remarked no change. 

Reynolds (British Journal of Photographyy 1861, p. 9) 
compares the relative action of the solar spectrum on paper 
impregnated with ferric oxalate, and that prepared with 
silver chloride. He found that the action of light was 
nearly the same. 

According to Eder, ferric oxalate is relatively more 
sensitive to the green than silver chloride. A mixture of 
ferric chloride and oxalic acid, or of oxalate, behaved in the 
same way. It was also the same when double oxalates of 
iron (ferricum) and ammonium, or potassium were used. 

Actinometers, in which ferric oxalate is used as a basis, 
give, according to Eder, a measure of the ultra violet, blue, 
and blue-green rays, the same results being obtained when 
ferric chloride and oxalic acid are used.* 

Marchand {Etude sur la Force Chimiqicey 1875) examined 
the action of the spectrum on a mixture of ferric chloride 
and oxalic acid, with which he had filled his photometer. 
He measured the action of the different rays by the 

♦ Eder's " Chemical Effect," chap. x. p. 65. 



qaantities of carbonic acid eliminated daring equal ex- 
posures. His results were as follows : — 


... 5-7 


... 9-9 


... 43-1 


... 184-1 


... 615-8 


... 370-0 


... 321-0 


... 52-1 

The work of Marchand showed (1st) that oxalic acid 
allowed all the rays to pass ; (2nd) that ferric chloride only 
allowed the red, orange, yellow, and green, and a very little 
blue ; (3rd) that a mixture of the two only allows the red, 
orange, yellow, and green to pass, without a trace of the 
blue. Marchand measured the intensity of the luminous 
action by a quantitative determination of the ferrous oxide 
produced, or by the quantity of carbonic anhydride dis- 
engaged during oxidation of the oxalic acid. It should, 
however, be stated that Becquerel contests the accuracy of 
the above results of Marchand, who defends his method 
against the former's criticism by saying that he did not 
wish to determine the chemical intensity of the light, except 
so far as it had acted on the liquid {Ann, Chem, Phys. [5] 
vol. ii. p. 160). As Eder also points out, in this method, 
the absorption of the carbonic acid by the liquid must be 
taken into account, this absorption varying with temperature 
and pressure, besides which, for small quantities, the process 
would be liable to give inaccurate resultSi 


Draper noticed that ammonio-citrate of iron (ferricum) 
brushed on paper is reduced as far as the blue-green to near 
F. Herschel remarks that a mixture of this salt and 
potassium ferricyanide rapidly becomes blue in the blue, 
in the violet, and ultra-violet, the blue rays having the 
maximum effect. A mixture of ferric chloride and tartaric 
acid exposed to white light and to coloured light in the 
same manner as the organic salts of iron already described, 
is less sensitive, according to Eder, than the oxalate. 

Ferric sulphocyanide in aqueous alcoholic or etheric 
solution, which is of a beautiful red colour, is reduced, 
according to Grottus, principally by the blue-green rays. 

Herschel (Hunt's Fhotography^ 1852, 3rd Ed. p. 56) gives 
some interesting experiments on the behaviour of some 
iron salts under the influence of heat — that is to say, the 
lower rays of the spectrum. Paper was washed with 
ammom'o-citrate of iron and potassium ferrocyanide in about 
equal proportions ; it was exposed to sunshine, washed, and 
dried. He then washed this paper with mercurous nitrate, 
and on exposing to a concentrated spectrum its whiteness 
was changed to brown over the whole region of the red and 
orange rays, but not beyond the luminous spectrum. 

Sir John also proceeds to show that the reduction of the 
iron salts is chiefly by the blue rays. A slip of paper prepared 
with ammonio-citrate of iron was exposed partially to sunshine 
and washed with bichromate of potash ; the bichromate is 
deoxidized and precipitated upon the sunned portion, just as 
it would be if directly exposed to the sun's rays. In a 
subsequent chapter will be found a fuller account of the 
experiments which we have made. 



OuB readers may have remarked that, in the early platinnm 
processes of Carranza, platinic chloride was used, this salt 
being variously known as bichloride of platinum of the old 
chemistry, or tetrachloride of the new : whereas, with the 
processes of Willis, the double chloro-platinite of potassium 
is used. In order to solve the question whether this was 
the best salt for the purpose, Pizzighelli and Hubl went 
through a variety of experiments, which we describe literatim 
from their book.* 

" In the process now before us the salts of platinum play 
a much more important part than those of iron, as from 
them is derived the metal of which the image is finally 
composed. As already stated, in the production of this 
image the salts are reduced ; hence only those salts of 
platinum are suitable which are capable of being readily 
reduced by the above-mentioned reducing agents, and 
which for this purpose require the use of comparatively 
small quantities of the ferrous salts. Further, as in 

* " Platinotype," pp. 26-29. 


sensitizing the paper the salt of platinum is applied simnl- 
taneonsly with that of iron, all those compounds of 
platinum are excluded from consideration which, in mixing 
with the salts of iron, may give rise to disturbing reactions. 
Of all the salts of platinum, the chloride, bromide, and 
iodide seem best to fulfil the first of these conditions ; while 
the sulphite, the double-cyanide compounds, and the double 
salts of ammonium and platinum are either not reduced at 
all, or are reduced with very great diflSculty. Independently 
of this, however, the first-named salts are to be preferred, 
on the ground that they can be prepared more easily, and 
are therefore cheaper. 

"The chemical reaction in the formation of the image 
is, according to Berkeley (Fhotographk Newsj 1882, p. 157), 
most simply represented by the following equation : — 

For platinous chloride — 

Ferrous Platinous Ferric Ferric to -«„„«» 

oxalate chloride oxalate chloride ^*aw»«™ 

6FeCj04 + SPtCls = 2Fe2(C204)3 + FesClg + 3Pt 

Analogous is that for platinic chloride- 
Ferrous Flatinic Ferric Ferric pi«*i„„«» 
oxalate chloride oxalate chloride ^'»"num 

12FeC204 + 8PtCl4 = 4Fej(C204)3 + 'FejOl^ + 3Pt 

" The correctness of these equations is, however, rendered 
doubtful by our observation of the formation of gas when 
the image is developed in a hot solution of potassic oxalate. 
Now, this reaction can only be due to the fact that the 
remainder of the oxalic acid, combined with the iron, is 
displaced by chlorine, and separates as carbonic acid in a 
gaseous form. We may therefore assume that the reaction 


is not quite so simple as the equations would indicate^ but 
is probably much more complicated. It should also be 
borne in mind that the platinum salt itself, as we have 
already had occasion to mention, undergoes a slight altera- 
tion under exposure to the light. 

" But whatever the real process of reduction may be, it is 
clear that the platinic chloride requires just twice as much 
ferrous oxalate for its complete reduction as the platinous 
chloride. This explains why it is scarcely a matter of no 
importance whether, with Willis, we employ for developing 
the image a platinous salt, or, with Eoninck and Eoppe, 
a platinic salt. The quantity of ferrous salt need not be 
so large in the first case as in the second ; and as the ferrous 
oxalate is only formed by exposure, the duration of that 
exposure may be considerably less when a platinous salt is 
used than is required in the case of a platinic salt. 

"As in every other photographic printing process, we 
find also in this that the more sensitive substance gives soft 
pictures with a hard negative, and with a soft negative 
weak pictures, while the substance requiring a longer 
exposure will give, in the one case a hard, in the other 
a brilliant, picture. It will, therefore, be more advisable to 
employ generally a platinous salt as a sensitizer, and to mix 
with it, when the negative is soft, a little of the correspond- 
ing platinic salt, or, when the negative is weak, a larger 
quantity of the latter. 

" According to our own experience, of all the platinous 
salts, the platinous chloride and the double salts of platinous 
bromide best comply with all the required conditions, and 
of the latter the platinous bromide of potassium is to be 


preferred. The doable salts of platinouB iodide cannot be 
nsed, as in mixing with the ferric oxalate salt they reduce 
it, with separation of iodine. The corresponding simple 
salts — ^that is to say, the platinons chloride and bromide — 
are insoluble in water ; before they can be used, therefore, 
they must be dissolved in solution of the corresponding 
haloid acid — ^a process which, as has already been explained, 
cannot be carried out on account of the free acid present. 

^^ Potassium chloro-platinite and the corresponding bromo- 
platinite possess the advantage of being easily prepared 
and purified ; but, on the other hand, the disadvantage that 
they cannot be mixed with platinic chloride and its double 
salts without the formation of an insoluble precipitate of 
potassium chloro-platinate. This defect is not found to 
exist in the case of sodium, lithium, and magnesium double 
salts ; but the first two crystallize only with difficulty, and 
it is on that account troublesome and costly to obtain them 
pure. Besides, they are hygroscopic and deliquescent in a 
high degree ; and as the quantity of water they contain is 
so variable, they cannot be accurately weighed without 
special arrangements and precautions. The magnesium 
salt is not deliquescent ; but it does not readily crystallize, 
and cannot, therefore, be easily obtained in a pure state. 
The calcium, barium, and strontium salts cannot be used, 
from the fact of their forming insoluble precipitates with 
ferric oxalate. 

'^ A consideration of the comparative advantages and dis- 
advantages possessed by the above-mentioned platinum 
compounds, leads us to give the preference to the potassic 
salts ; and, as the preparation of the potassium bromo- 


platinite is much more troublesome than that of the corre- 
sponding chloro-platinite, we determined to carry on onr 
experiments with potassium chloro-platinite. We desire, 
however, to draw attention to the circumstance that, accord- 
ing to our experiment, the double salts of potassium, sodium, 
lithium, and magnesium all give identical results in the 
production of the image, both as regards their reducing 
powers and as regards the appearance of the finished picture. 
"When preparing a sensitizing solution of chloro-platinite 
of potassium, adapted to the character of the negative from 
which the copy was to be taken, we were compelled to leave 
out of the question the direct addition of a platinic salt, 
partly because a mixture with the double salt of platinic 
chloride is not feasible, and partly on account of the 
difficulty and expense of preparing a more suitable platinic 
salt. But we tried whether the required advantage could 
not be obtained by adding the oxidizing substances, which 
have not the effect of unmediately decomposing the sen- 
sitizing solution, but only convert more or less of the 
platinous into the corresponding platinic salt at the time 
when the solution dries up on the support." 

The Substances suitable for the Development of 

THE Platinum Image. 

If paper coated with ferric oxalate and chloro-platinite of 
potassium, or ferric oxalate alone, be exposed to light, and 
then treated with hot or cold water, or in the second case 
treated with chloro-platinite of potassium or platinum tetra- 
chloride in water, no image, further than the already existing 


one f onned directly by the action of light, will be formed. 
As a matter of fact, the ferrons oxalate in presence of 
moisture has a slight reducing action, but it is so slight that 
the image will be dissolved out by the water before it is 

In this respect the action of the iron salts is different to 
that of the silver ones, for there, as we see in Carranza's 
process with platinum tetrachloride; or Clark's with platinum 
chloro-platinite, nothing more than an aqueous solution of 
these salts is necessary to bring out a strong platinum 

Willis, in his hot-bath process, floats the paper over a hot 
solution of oxalate of potash, or, in his cold-bath process, 
with oxalate of potash and disodic orthophosophate. 
Besides the oxalate of potash, there are many substances that 
are capable of acting as developers ; some act best when 
applied hot, or some cold ; they will even act, in the presence of 
moisture, when they are contained in the coating ingredients 
of the paper itself, as in Pizzighelli's new process. 

These devehpersy as they are usually called, have been 
carefully investigated by Pizzighelli and Hiibl, and we give 
the results of their experiments. 

Developers are used both in the hot and cold bath pro- 
cesses ; in the former they act really like a gelatine plate 
developer — that is to say, they in no way go to make up the 
structure of which the image is built, but simply act as a 
vehicle or conveyance between the provisional and resultant 
image. In the cold-bath process, however, the developers 
themselves contain the platinum salt or colouring matter. 
It will be, therefore, readily understood that a different set 


of chemicals may be reqnired for the one process from those 
used with others. We shall, therefore, commence by treating 
of those used with the old or hot-bath process. 

Although this process is always known as a hot process, it 
does not by any means follow that cold developers cannot 
also be used in it ; in fact, when we come to the practical 
details of the process, we shall see that certain advantages 
are gained by using the solution cold. In the following list 
of developers, which are given in the order of their reducing 
power, they are, with the exception of Nos. 11, 12, and 15, 
applied in solutions at a temperature of 80^ C, the solution, 
when not otherwise specified, being concentrated. 

The experiments were carried out by exposing strips of 
paper under a graduated scale to the same light, for the same 
time, and comparing the results obtained both as regards 
the number of gradations brought out — ^that is, the rapidity 
— and also the opacity or quantity of platinum salt reduced. 

1. Sodium acetate: very energetic, giving soft pictures 
with a yellow tinge, owing to formation of basic ferric 
acetate, but can be discharged by subsequent treatment with 
hydrochloric acid, or minimized by strongly acidulating the 
developer with oxalic or citric acids. 

2. Sodium acetate and oxalic acid: acts same as No. 1, 
but gives pure whites. 

3. Potassium citrate .- behaves most identically with 2. 

4. Sodium carlonate (hot) : acts much the same as the 
above, but forms yellow-coloured basic-ferric salts; an 
insoluble precipitate is also formed in the developing bath. 

5. Ammonium citrate (neutral) gives the same result as 
above, but without basic precipitate. 


6. Ammonium citrate (acid) as used for developing chloride 
of silver pictures : same results as No. 5. 

7. Potassium oxalate : ditto. 

8. Rochelle salt : ditto. 

9. Ammonium henzoate: same as No. 4. 

10. Sodium succinate : ditto. 

11. Caustic potash (cold, sol. 1 in 25) : much inferior in 
power to the above. 

12. Sodium carbonate (cold) : ditto. 
1^. Sodium phosphate (cold) : ditto. 

14. Wai&r (hot)\ 

15. Ammoni^i \ P^«s^«« ^^^7 ^ moderate power of 

16. Oxalic add ) developing. 

The different citrates are practically too expensive, and 
give no compensating greater advantages over the rest, and 
are therefore out of the field. All the latter developers from 
Nos. 11 to 16 are too weak in their action to be of any use. 
Of the remaining mixtures, the sodium acetate, potassium 
oxalate, and Eochelle salt are the best, but Hiibl and 
Pizzighelli give preference to the potassium oxalate, and as 
this salt is the one that is recommended by Willis in his 
practical working instructions of the process, it may be 
fairly assumed that it is the best. 

The Effect of the Presence of Foreign Bodies in 
THE Sensitizing or Developing Solutions. 

It is hardly necessary to point out that it is always a 
necessity to keep the different ingredients used in all sorts 
of platinotype processes absolutely free from foreign bodies, 
and also, to ensure the best results, that chemicals of the 


most absolute purity should be obtained. There are many 
substances that act, even when present in small quantities, 
very vigorously on the platinotype image ; in fact, the 
mere difference between alkalinity and acidity, whether of 
the sensitizing or developing mixtures, produces decided 
differences in the result. 

Generally speaking, the sensitizing solution should have 
an acid reaction in order to prevent the formation of any 
insoluble basic iron salts, which give to what should be 
the whites of the picture an unpleasant yellowish tinge, 
which often is not removed by hydrochloric or other acids ; 
but, at the same time, excess of acid is also to be avoided, 
as this hinders the substitution of the iron and platinum in 
the development. 

With regard to the state of the developer, Pizzighelli 
recommends that this should be kept distinctly acid ; but 
the Platinotype Company, in their instructions, lay special 
stress on the fact that on no account should any acid be 
allowed to get into the developer, which should be kept 
distinctly neutral We must confess that we entirely agree 
with the Company, and consider that the solution should be 
kept neutral. The presence of any acid in the developer is 
apt to cause granularity in the print. When a hot develop- 
ment is used, there is but little time for this to show, but if 
the development be effected with tepid or cold solutions, 
when the process naturally takes much longer, this is sure 
to make itself evident. Its cause is probably to be found 
in the fact that the acid bath is capable of dissolving out, 
or rather commencing to dissolve out, the provisional iron 
image before this has had time to reduce the platinum salt. 


We have even found it advantageous to render the bath, 
when the development is effected with an absolutely cold 
(60° F.) solution, distinctly alkaline with ammonia. In 
this case, no insoluble basic iron salt appears to be formed 
in the paper. On the addition of the ammonia to an old 
bath containing iron, a precipitate is at once formed, which, 
however, is redissolved by the same bath almost immediately. 
We therefore reconmiend that with hot development the 
bath be kept neutral, and with cold development rendered 
slightly alkaline with ammonia. 

In using the term acid as applied to the sensitizing 
solution, it must be remembered that ferric oxalate, like 
many other of the acid iron salts, gives an acid reaction in 
itself when pure, and, therefore, considering it as a neutral 
is not strictly correct. At the same time, acids may be 
found present in carelessly prepared chloro-platinite of 
potassium, and as the presence of any mineral acid is highly 
injurious to the formation of the image, the salt, if 
purchased, should be carefully tested for a neutral reaction. 
At the same time, Pizzighelli recommends the addition of 
6 or 8 per cent, of oxalic acid in the sensitizing solution, 
and the addition of an inorganic acid does not appear to 
affect the ultimate result. 

Pizzighelli states that the presence or absence of acid 
affects the colour-tone of the pictures, a neutral sensitizer 
giving a brownish picture, and an acid one a bluish picture. 
These results would therefore agree with the observations of 
Gwenthlian, but we cannot, however, agree with either of 
these authorities, at least as regards the toning of silver 
prints ; here the presence of alkaliis or acids has no action 


on the resalting colour. The only thing, besides of conrse 
the addition of other chemicals, that affects the colour-tone 
is, in our experience, the composition of the sizing of the 
paper. It is, of course, possible that the acid in the sensitiz- 
ing solution may tend to destroy some of the sizing in the 
platinotype paper, and so cause the phenomenon that 
Pizzighelli describes ; we ourselves have, however, never 
met with it. 

Reducing Substances. 

The presence of any of these — with the commoner ones, 
such as hyposulphite of soda (sodium thiosulphate), formic 
acid, sulphurous acid, chromic acid — should be carefully 
avoided ; they tend both to reduce the ferric oxalate and 
the platinum, and therefore cause fogging in the high 
lights. Their presence appears to be injudicious, even when 
in the smallest proportion. 

Oxidizing Substances. 

The action of these substances is, of course, directly the 
opposite to the above ; they tend to undo the action of 
light, reconverting the ferrous salt formed by the agency 
back again to the ferric stage. They have also probably an 
action on the platinum salt itself, converting this also from 
a platinous into a platinio salt, the precise chemical form 
it takes being probably the insoluble potassium chloro- 
platinate. When any platinic salt is present, it requires 
twice as much ferrous salt to replace it as does the platinous 
salt. Since the quantity of the platinic salt is, by the 
addition of an oxidizer, equally formed over the whole 


Burface, whereas the ferrous oxalate, or the reducer, is 
formed only ly the action of lights it follows that in the high 
lights, where the formation of ferrous oxalate is very slight, 
the platinie salt is relatively largely present ; but in the 
deep shadows, where the ferrous salt is plentifully formed, 
the amount of platinum remains constant, and is relatively 
a small part of the whole. Therefore, on development, the 
presence of the platinie salt is but slight in the shadows, 
but relatively great in the high lights, and the print gains 
in brilliancy, or if the platinie salt be present in large 
excess, positive hardness may result. 

But any oxidizing chemical in any proportion can be 
practically used for this purpose, provided they do not 
form chloro-platinate in the mixture, which, once formed, 
could not be evenly applied to the paper. It is there- 
fore generally accepted that chlorate of potash is the 
best oxidizing substance to use ; it appears to be almost 
without effect on the solution, only acting when this is dry. 
The explanation of this is that the first action of the 
chlorate of potash on the iron salt is the formation of ferric 
chlorate ; the salt is, however, unstable, and gradually, 
during drying, hands over its oxygen to the potassium 
chloro-platinite. The action of chlorate of potash is, how- 
ever, very energetic, and it must be added with great care 
and scrupulous exactitude. The presence of such a minute 
quantity as one-hundredth per cent, is said to make itself 

1. If the sodio-chloro-platinite be used instead of the 
potassium salt, in that case, sodium-chloro-platinate can be 
directly added instead of chlorate of potash. 


Very great power is in the hands of any person who 
prepares his own paper ; by a suitable proportion of this 
salt a perfect gamut of results from softness to hardness 
can be obtained, and the paper prepared to suit the 
character of the negative to be printed from. 

( 61 ) 



Part I. 

Choice of the Paper or Support, 

Almost any quality of paper, providing it be free from 
metallic or other impurities, can be used for platinotype. 
At the same time, the acid bath to which the print has to 
be subsequently treated has a great tendency to rot the 
texture of the paper, making it easily torn in the subse- 
quent handlings. It is, therefore, advisable to choose a 
somewhat heavier paper than the ordinary brands of Kive 
and Saxe, used for silver printing. 

The state of the initial sizing of the paper has an 
important influence on the resulting print. The sensitizing 
solution in platinotype might almost be considered to be 
in the form of an emulsion, and is smeared or spread over 
the surface of the paper, and it is, therefore, necessary to 
keep the solution as much on the surface of the paper 
as possible. If a paper almost unsized — say, such as 
plate paper — ^were used, it should be treated to a supple- 
mentary sizing before the sensitizing solution is applied. 


or it will all sink into the body of the paper, and give weak 
and flat images. At the same time, the majority of papers 
that one is likely to experiment with are already sized 
sufficiently to dispense with the preliminary coating, 
but some gelatine or arrowroot must be added to the 
sensitizing solution, or the platinum black will wash off. 

More mistakes are apt to happen in the correct sizing of 
the paper than in any other portion of the manipulation, 
different brands of paper requiring different treatment. 
The point to aim at is to sufficiently close the pores of the 
paper, to prevent the sensitizing solution sinking in, but 
at the same time to leave them sufficiently open to enable 
the platinum to attach itself to the paper, and not fall off 
into the developing bath. 

The Platinotype Company themselves sell one or two 
different marks of paper, particularly suitable for the pre- 
paration of platinotypes. These papers are probably resin- 
or arrowroot-sized, these substances having certain advan- 
tages over gelatine, which is coagulated by the salts of 
platinum, and is apt to work in streaks. Pizzighelli recom- 
mends a paper made by Gustav Eoder and Go., of No. 10, 
Wallfischgasse, Vienna, at their mills at Marchendorf , called 
ivory vellum, which may be obtained either ^^?iot pressed ^^ or 
" noV^ Eough papers, such as Whatman's rough drawing- 
papers, are not very suitable for platinotype ; there is a great 
difficulty in spreading the solution on them, as it has a 
tendency to be brushed off the tops of the granules into the 
valleys, causing the print to turn out very rough, granular, 
and uneven.* 

* The Platinotype Company now appear to have overcome these 


Perhaps the best procedure to follow in such a case is to 
apply a ten or twenty per cent, solution of dextrine to the 
paper before sensitizing it. This forms a temporary coating, 
and keeps the sensitizing solution on the surface, but gives 
no hard or shiny appearance to the paper, as it is largely 
removed in the subsequent washings. 

Part II. 

Preparation of the Paper. 

For an average paper, such as a heavy Saxe or Eive, or 
a Whatman's No. 1, the following is the proportion of the 
sizing solution it is advisable to apply : — 

Gelatine (any good brand will do, such 

as Nelson's coating gelatine) ... 10 grains. 
Water ... 2 ounces. 

The gelatine is allowed to soak thoroughly till swollen ; 
it is then dissolved by gentle heating, and 3 grains of 
powdered alum are added and ^ ounce of methylated 
alcohol. It should be filtered hot through a jelly bag or 
canvas, taking care that no bubbles are formed. The above 
solution should hardly solidify at 70° F. 

Arrowroot. — ^The same amount is to be used, the flour 
being first rubbed up with a little water till it forms a stiif 
paste, and 2 ounces of hot water are added with careful 
stirring, and brought up to the boiling point, when the 

arrowroot will lose its milky colour, and become transparent 


difficulties, and sell a sample of extremely rough paper of great purity 
and exceUence. 


and gelatinous in its consistency ; ^ omice of alcohol is 
added, and, after straining, the size is ready for use. 

Either of the ahove sizes are applied by immersing the 
sheets bodily in the solution spread out in a flat dish. A 
little care is necessary in this operation to avoid air-bells, 
the best way being to plunge the piece of paper into the 
solution, beginning at one edge, then turn it over, and with 
a glass triangle break any bubbles that may form. After 
a couple of minutes* immersion, it should be drawn out 
slowly and steadily without making any stoppage ; in this 
manner the superfluous liquid will be left in tbe dish, and 
not be carried off on the surface of the paper. The paper 
should be hung up to dry in a warm room, or before a 
stove ; if the room be too cold, the gelatine will be found 
to set in a line along the bottom of the paper, instead of 
dripping off as it should do. In any way, as the gelatine 
or arrowroot will have naturally gravitated down to the 
lower end — ^which will be, therefore, more highly sized than 
the top— it is advisable to repeat the above operation, 
reversing the paper end for end during the drying. 

Heavy papers should not be immersed in the solution, 
it being quite suflBcient if they be simply floated, and left 
for a minute or two on it ; it is still advisable, however, 
to size them twice, reversing the position in which they 
are dried. 

Although not so successful in its results, still it is prac- 
ticable to simply brush the sizing on the surface of the 
paper, and to let it dry ; this method will be found useful 
where it is required to only sensitize a single sheet of paper. 

Another very excellent way of dealing with the finest 


sorts of stu£fs or papers — snch as sarsenet, or the Japanese 
rice papers, or India papers — is to first mount them bodily 
on a thicker paper by means of dextrine, and in this con- 
dition to sensitize, print, and complete all the operations. 
The picture, when finished, can be removed from its mount 
by warm water, in which the dextrine is of course soluble. 
In this manner the very fiimsiest of materials can be 
successively handled. 

Pr^aration of other Supports. 

Limn and other Fabrics. — ^The procedure to follow with 
these materials does not essentially differ from that when 
paper is used. A little care has to be taken with these 
stuffs, to see that they do not crease or dry in stiff folds 
from the action of the size. They should, whilst still wet 
from the second sizing, be stretched on light wooden 
frames, in which state they will dry perfectly flat ; the 
sensitizing liquid can also be most conveniently applied 
to them whilst they are still stretched on their frames. 

Preparation of Wood. 

Soft and Hard Woods. — ^The surface of wood to receive 
the sensitizer must be carefully and evenly smoothed. If 
the wood has to be impressed with a picture for merely orna- 
mental purposes, the above sizing solution can be applied 
to it, and then be allowed to dry ; a little care may be 
necessary to prevent the wood warping, and as soon as the 
surface moisture has evaporated, it should be placed under 
pressure, when it will be found to dry straight. 


If the wood is to form a basis for the graver's tools, it is 
important to moisten it as little as possible, as any damp 
rots the fibres, and makes the catting of the fine lines very 
difficnlt. No sizing solution should be used, bnt the sensi- 
tizer, having as little moisture in it as possible, must be 
rubbed well into the block till dry. For the purpose in 
question it is not removed to get an even surface, nor is 
the same vigour necessary, and no difficulty should be found 
in preparing boxwood blocks. The cold development is 
more suitable for the purpose than the hot ; in fact, to use 
an Irishism, the hot bath should be worked cold, the 
surface being merely moistened with the cold oxalate 

[Although the above instructions may be useful to persons 
abroad, or who wish to prepare some special kind of paper 
fabric, or substance for platinotype printmg, it must not be 
forgotten that suitably ^ized papers (special quaUties, "hot- 
pressed," "not" rough, and also different sorts of fabrics), 
can be obtained from the Platinotype Company, all ready 
sized ; m this state they are, of course, practically unalter- 
able,^and can be sent without danger to any part of the 

Part III. 

Preparation of the Ser^simng Solution. 
mtnerto we have been dp 1" 
that are entirely unaffected bTlLT'^ T^^ °^"^ 
operations can very weU be • previons 

and the simply sized paper ca^"^ °^*' ^^^^ "^ exaahiae, 
stored away in any quantit *^' °' *^°^ir8e, be prepared and 

y. and is practicaUy unaltered by 


time. But the operation of sensitizing must be performed 
in a suitably lighted or rather darkened apartment. The 
sensitizing solution is decidedly more active to the feeble 
rays of light than is ordinary silver paper, and as no change 
is visibly shown of the first commencement of reduction, it 
is advisable by a few trials to assure one's self of the safety 
of the coating room. Yellow light is unsuitable for coating 
the paper, owing to the colour of the sensitizing mixture 
being the same, it thus being difficult to distinguish the 
coated from the uncoated parts, and streaks may result. A 
really good paraffin lamp will, however, give a light nearly 
white enough, although weak daylight filtered through 
white tissue paper is preferable. In all cases the paper 
should be exposed as little as possible, and during the 
drying should be carefully protected from all white light. 

The preparation with which the paper, is coated, consists 
of a mixture of chloro-platinite of potassium and ferric 
oxalate, to which may be added, to obtain certain effects, 
chlorate of potasL The chloro-platinite of potassium, the 
making of which requires a good laboratory, and some 
chemical knowledge, should be preferably bought ready 
prepared, it being now obtainable from all large chemists 
and photographic dealers. In the Appendix we give, how- 
ever, full directions for its manufacture from metallic 

The ferric-oxalate solution, even if bought from the 
chemist, demands a certain amount of quantitative analysis, 
as otherwise it is impossible to estimate its strength ; we 
therefore give here in full, Messrs. Pizzighelli and Hiibl's 
method of manufacturing and estimating this. 


Preparation of (ke Ferric-Oxalate Solution. 

For the preparation of the solution of ferric oxalate the 
following operations are necessary : — (1) Manufacturing the 
ferric-hydrate ; (2) dissolving the substance in oxalic acid ; 
(3) determining the amount of iron and of oxalic acid 
contained in this solution ; (4) diluting and acidulating the 

The method of preparing ferric hydrate is generally well 
known, but, for the sake of completeness, we will give a 
brief description of it. Five hundred grams of ferric 
chloride are dissolved in from five to six litres of water, 
and, when the solution has been brought to the boiling 
point, a solution of soda is added until it gives with litmns 
paper a distinctly alkaline reaction. For this purpose about 
250 grams of caustic soda will be found necessary. The 
precipitate is then washed with hot water by decantation 
until the wash-water is no longer alkaline. It is next placed 
in a cloth, and, by pressure, freed from the greater part of 
the water. With the ferric hydrate thus obtained, which 
ought to have a syrupy consistency, there should be mixed 
about 200 grams of finely crystallized oxalic acid, and the 
mixture be then left to itself for a few days at a temperature 
of not more than SO*' C, and in a place completely protected 
from the Ught ; under these circumstances the formation of 
ferric oxalate will go on steadily. Some persons recommend 
the promotion of this process by digesting the mixture for 
some time at a high temperature ; this we are decidedly 
opposed to, since, by heating for even a few hours to 50° or 
60° C, the salt will be partially reduced to ferrous oxalate. 


At the commencement the solution has a pure green colour ; 
by continued cooking it turns yellowish-green, and finally 
greenish-brown. When this moment has arrived, the remain- 
ing ferric hydrate should be filtered off, and the solution be 
submitted to quantitative chemical analysis.* 

Although the determination of the amount of iron and 
oxalic acid contained in the solution is one of the simplest 
of analytical operations, we tried at first to dispense with it» 
Closer investigation, however, proved to us how necessary 
it is- to confine the relations between rather narrow limits, 
in order to ensure the success of the platino-f erric process. 
Now, as ferric oxalate cannot be prepared in a stable form, 
so as to have a constant composition, there remains no other 
way than that of determining the composition of the 
solution by analysis, and then diluting it to the required 
degree. Further, it should be noted that any quantity of 
the solution may be prepared at once, and then kept in 

From the analysis we ascertain the quantity of ferric 
oxalate contained in 100 of the solution, as well as 
any slight excess of oxalic acid which happens to be present. 
Tbe liquid is then diluted with so much distilled water 
that every 100, of it may contain 20 grams of ferric 
oxalate [Fe2(C204)8]. Crystallized oxalic acid is then added, 

* To perform this analysis a few cubic centimetres of the solution are 
measured off, and the oxalic acid then determined from measure by means 
of permanganate of potash ; the amount of iron in the same liquid may be 
ascertained in the same way, after reduction by means of zinc. But it is 
perhaps more conyenient to determine by weight the iron in a separate 
portion of the solution ; this can be done by eyaporating, heating to red- 
ness, incinerating with nitrate of ammonia, and weighing the ferric oxide 
which remains. 


until, with the free acid akeady in the mixture, that 
substance amounts to from 6 to 8 per cent, of the ferric 
oxalate already in the solution — ^the normal ferric solution. 

An iron solution purchased from the chemist must be 
tested in the following manner before it is used : — It must 
not turn blue with a solution of f erricyanide of potassium 
(red prussiate of potash). When boiled and diluted with 
ten times its quantity of water, it must not become turbid. 
From the first reaction we ascertain the absei^ce of ferrous 
salts ; from the second, that of basic ferric oxalate. 

In order to introduce into the sensitizing solution some 
chlorate of potash, which in certain circumstances is neces- 
sary, the best way is to keep ready for use a mixture of 
chlorate and ferric solutions. It can be prepared by 
measuring oflF a certain quantity of the normal ferric 
solution, and mixing with it so much chlorate of potash as 
to cause 100 of the Uquid to contain 0*4 gram of 
the salt. This is the normal chlorate of iron solution. 

Both the ferric solutions must be kept away from the light. 

Another method of preparing ferric oxalate is given by 
Weissenberger {Phot Mittheilungen,TSo. 400 ; and Bull Balge 
de Photy vi., N. S., p. 960). Dissolve 40 grams of anhydrous 
ferric sulphate in 400 of hot water, then add 86 drams 
of pure crystalUzed sodium carbonate dissolved in 200 com. 
of hot water. A precipitate is thrown down, and this is to 
be washed until the last water gives a neutral reaction to 
Utmus. 49 grams of powdered oxalic acid have then to be 
added to the precipitate, which should all dissolve with 
evolution of carbonic acid gas. When ebullition has ceased, 
and all precipitate is dissolved, make up the bulk with water 


to 187 ccm. This solution should then contain 20 per cent, 
of ferric oxalate and 6 per cent, of free oxalic acid. (We 
might mention that we do not quite understand how 
Mr. Weissenberger succeeds in dissolving his ferric sulphate 
in the quantity of water given.) 

The Sensitizing Solution, 

The precise proportions of the substances composing this 
depend somewhat on the effect wished for — ^that is to say, 
whether a hard or a soft print is to be obtained. 

We have the following stock solutions : P — One part by 
weight of chloro-platinite of potassium is dissolved in six 
parts of distilled water, and labelled stock solution. A and 
B — the ferric oxalate and the mixed ferric oxalate and 
chlorate of potash solution (described in previous page). 
The standard size for platinotype paper is 26 by 20 inches, 
or, in French measures, 50 cm. by 66 cm., and such a 
surface should require about 10 cubic centimetres or grams 
of solution (the amount is equivalent to 154 fluid grains, 
or 168 minims). 

This is the quantity given by Pizzighelli. The Platino- 
type Company, on the other hand, put down 140 minimt^ 
as being the average quantity. This discrepancy is easily 
explained by the different texture of the paper used. It is 
clear that certain papers must require more than others, 
and, therefore, these amounts are merely indications. 

For soft results, but with rich blacks : — 

P or Platinum solution ... 24 ccm. or 6 drams. 
A or Perric-oxalate „ ... 22 „ or 5i „ 
Water 4 „ or 1 dram. 


DifltiUed water quite free from Ume or iron must be used. 

To get greater brilliancy, use — 

p or Platinum solution ... 24 or 6 drams. 
A or Ferric-oxalate „ ... 18 „ or 4i „ 
B or Ferric-chlorate „ ... 4 „ or 1 dram. 
Water ^ » ^^ ^ " 

To obtain results corresponding to silver images :— 
p or Platinum solution ... 24 or 6 drams. 
A or Ferric-oxalate „ ... 14 „ or 3i „ 
B or Ferric-chlorate „ ... 8 or 2 „ 
Water 4 „ or 1 dram. 

For very weak negatives : — 

P or Platinum solution ... 24 or 6 drams. 

A or Ferric-chlorate „ ... 22 „ or 5i „ 

B or Water 4 „ or 1 dram. 

The lessening of the amount of platinum present, or rather 
its replacement by water, will have the effect of giving very 
soft prints with no blacks, resembling pencil drawings, and, 
as such, are most suitable for being subsequently coloured. 

On highly sized and hard papers the small amount of 
water may be totally omitted. 

Platinotype Company's Instructions. 
The above proportions are those given in PizzigheUi and 
Hiibl's work on " Platinotype," but, for the convenience 
of purchasers residing abroad, the Platinotype Company 

lemc oxalate is sold in two solutions, known 


respectively as Iron Solution A and Iron Solution B. By 
varying the proportion of these, harder or softer effects may 
"be obtained. The following are recommended : — 

For good half-tone, suitable for brilliant negatives, with 
strong contrasts : — 

Iron Solution A 1 part. 

For a harder effect, suitable for thin or weak negatives : — 

Iron Solution A 1 part. 

,, ,, xj ••• ••• ••• ••• o uaruc* 

By increasing the proportion of A, a tendency to hardness 
or destruction of half-tone is obtained. By increasing the 
proportion of B, on the contrary, a tendency to produce 
flatness, or all half-tone, is given. If A is present in 
quantities of less than one-eighth, there will be a tendency 
to get stained or fogged whites. 

To the above solutions, of whatever proportion made up, 
there is added chloro-platinite of potassium in the proportion 
of 1 dram (60 grains) to each fluid ounce, or 1 in 7*3. 

A comparison of the quantity of platinum used in this and 
Pizzighelli's formula is interesting. 

Pizzighelli gives, in 50 parts of solution, 24 parts of 
platinum solution of 1 in 6 — that is equivalent, then, to 4 
parts of the salt in 50, or 1 in 12^ ; whilst the Platino- 
type Company recommend a strength of 1 in 7i, or nearly 
twice as much. It must be remembered that, whereas 
Pizzighelli's amounts were chiefly adduced from theory, 
Willis has had a much larger experience, and there is no 
doubt that by increasing the quantity of platinum the 


tendency is to give better images, more visible is the printing- 
frame, and of richer colours. 

It must be borne in mind, however, that the above 
solutions, however mixed, will not keep long, and, therefore, 
only the quantity likely to be required should be made up. 
The solution will only keep in hot weather about ten 
minutes, or in cold weather perhaps twice as long. 

Pabt IV. 
Coating the Paper, 

The operation of coating the paper may be shortly described 
by saying that the paper is laid down flat, the measured 
amount of sensitizing solution is then poured on, and brushed 
equally over the surface ; the paper is then dried. 

It is evident that these manipulations may be carried on 
in several ways, and any one used to coating such surfaces 
may proceed in his usual manner. For those who have no 
experience, the following hints may be found useful. 

To keep the Paper Flat during Coating. 

Pizzighelli recommends the following system. The paper 
is laid down on a sheet of glass about the same size as itself, 
but whose comers have been cut off. The comers of the 
paper are then nipped by wooden American clips. These 
clips are attached by indiarabber bands to pins on a drawing- 
board or other support of larger dimensions than the glass 
sheet. In this manner the clips holding the paper always 
tend to stretch it equally away from the centre, and, although 
the paper expands, it still retains its flat position. 



A slightly different plan has also been suggested — very 
stdtable where smaller pieces of paper are coated — and that 
is to chp the top of the sheet of paper laid out on a sheet of 
glass by a wooden or glass toggle clip. Such a clip i8 
infltantly constructed by the aid of an indiarubber band. 


The glass chp is, of course, made the full width of the 
paper to be coated, and, therefore, holds the whole of one 
end of the sheet firmlj. The left hand is then used to hold 
the bottom of the sheet extended, whilst the right hand does 
the coating. If it be preferred, the two systems can be 
combined, and, whilst the top end of the sheet is held by one 
broad clip, the two bottom ends can be extended by the 
elastic American clips. 

Beginners will do well to commence by coating small 
sizes of paper, say, 13 by 10 — that is, the quarter of the 
whole sheet of platinotype paper, 26 by 20 (half double 
elephant).- Such pieces can be conveniently coated by 
donbhng half an inch at each end under a piece of 12 by 10 
glass, and bo held securely. 

77*6 Pad, 

It ia important that no pressure be exerted on the sorface 

of the paper, or its texture may become abraded when, the 

sizing being removed, the sensitizing salt will sink more 


deeply into the paper at this spot, and cause a degradation 
of vigonr in the subsequent image. The pad should there- 
fore always be made of some yielding material, such as 
pure cotton-wool, or swansdown calico, or good flannel, and 
all hard or projecting surface be guarded against. Many 
ways will at once suggest themselves : a light roll of 
swansdown calico may be made, and the end of the cylinder 
used ; or a ball of flannel stuifed with cotton-wool ; or even 
a little pellet of cotton-wool may be taken between the 
Angers and used for small sizes. 

A variety of the Blanchard brush, as proposed by Mr. 
Lyonel Clark, is very useful where large sized pieces of 
paper are to be coated. A sheet of fairly thick celluloid, 
such as is used for film photography, is taken ; on it is laid 
a packing of cotton-wool ; and, lastly, a strip of swansdown, 
the swansdown being longer than the celluloid. The three 
are then doubled back without folding, the overhanging 


"^^OOlr^ ■AND. I 

Fig. 2. 

ends of the swansdown folded over the celluloid, and then 
clipped between two pieces of wood or glass that are sprung 
together with a broad indiarubber band, and which pieces 
serve as a handle. The celluloid gives the necessary stiff- 
ness without rigidity, whilst the packed swansdown makes 
a capital spreader. 


Whatever be the nature of the pad used as a spreader, it 
must not be used more than, say, a quarter of an hour at 
a time, or preferably even less. The outer coating should 
go into the residue tub, whilst even the inside packing 
should be washed in acid and water. This last may be 
avoided if, in the modified Blanchard brush, a thin sheet of 
oilskin be placed between the outer swansdown and the 
cotton-wool packing. 

A]pplying the Solution. 

The paper is laid sized side uppermost (and this side 
may be distinguished by the fact that in the rough paper 
the rougher, and in the smooth paper the smoother surface, 
are the sized •), and the measured quantity of the mixed 
solution is poured on to the centre of the sheet ; the pad 
is then applied, and with a circular motion, with the 
strokes spreading each time more outward, the entu*e sur- 
face of the paper is lightly gone over, taking care to see 
that every portion of the paper is covered. The direction 
of the motion is then changed, and up and down strokes are 
given so as to cross the sweeps at right angles, and so obviate 
every chance of the coating having a tendency to dry in 

In coating large sheets, it may be advisable to coat portions 
at a time, pouring a little on at one comer, smoothing that 
off, then doing another eone, and so on till the whole surface 
is covered. 

It is necessary to coat the whole surface of the paper^ 

* Pa^er sent ottt iti MIb h&s the sized side (mtwards. 


even if a vignette be intended, as where the sensitizing 
solution leaves oflF, the edges have a tendency to become 
reduced and subsequently dissolved ; but of course the same 
care need not be expended to see that the coating be as 
evenly applied at the edges as at the centre. 

No difficulty should be experienced in coating a sheet of 
paper evenly, as the operation is in reaUty very simple, being 
far more easy to perform than to describe. 

N.B.— About 20 minims extra of solution per 26 by 20 
sheet should be taken, when coating the first sheet, to allow 
for the absorption of the fluid by the pad. 

Part V. 
Drying the Paper, 

Some little difficulty, and some loss of paper, may be met 
with at this point, as it is important that the paper be in a 
certain condition before it be dried, and therefore the 
instructions should be carefully followed, and even a few 
experimental pieces may be profitably wasted. 

The drying divides itself into two operations, both of 
which should take a more or less fixed period of time. The 
first stage is what may be called the surface drying ; this is 
allowed to take place spontaneously, the paper being hung 
up for the purpose by one end, or preferably, laid down, 
sensitized side uppermost It should on no account be hung 
over a rod. This first drying is simply the evaporation of 
the surface moisture ; this should take not less than five« 
and not more than ten minutes. If, through excessive 
climatic dryness, the paper becomes desiccated too soon. 


artificial means mnst be resorted to to keep the paper damp 
a longer period. The second drying operation takes place 
by artificial means, even in the hottest climates, as it 
is most important that it be not only quickly but very 
thoroughly performed. 

The sheet of paper then, as soon as the surface moisture 
has disappeared, is held in front of a fire, or over some gas 
or paraflBn burners, till the remaining moisture is rapidly 
and completely removed. This drying point is indicated 
by the change in the colour of the surface, which from a 
pale lemon changes to a deeper saffron hue, and the paper 
becomes crackly to the feel. Care, of course, must be taken 
not to scorch the surface of the paper ; but short of this, the 
drying may be as rapid as possible. 

And now a few words as to the reason of this care in 
drying. It is very evident that the result sought for is to 
obtain as much of the sensitive salt on the very surface of 
the paper as possible ; but, at the^game time, it must have 
sufficient hold of the paper not to be washed off in the 
subsequent operations. 

Now, if the paper be dried or allowed to dry too quickly, 
the solution will not have had time to solder itself, so to 
speak, to the paper, and in the subsequent operation, will all 
fall off in the hot developing bath. Whereas, on the other 
hand, if too great a time be allowed to elapse, the solution 
will have a tendency to sink right into the paper, and the 
resulting prints will be flat and foggy. Hence the necessity 
of adhering pretty closely to the above rules. 





Oedinaby printing-frames are, of course, equally available 
for platinum printing. It is, however, necessary that an 
indiarubber pad be placed at the back of the paper to 
guard it against damp during this operation. Ordinary 
thin sheet indiarubber, such as is sold at all indiarubber 
stores, is the most suitable for this purpose. It should be 
the full size of the printing-frame, so as to thoroughly 
protect all portions of the print. The ordinary rubber- 
covered fabrics of which mackintoshes are made can be 
used for this purpose, but they are decidedly inferior to 
the indiarubber sheeting. This, moreover, makes a nice, 
soft pad, and, if a plate-glass printing-frame be used some- 
what larger than the negative itself, platinum prints can be 
left with impunity over-night, even in a damp atmosphere. 
ParafSned paper may also be used at a pinch, but it is not 
so pleasant to work with as the indiarubber. We cannot too 
strongly insist on the necessity of keeping the paper dry 
if prints with rich, juicy blacks and pure high lights are 
sought for. 



Whether the paper be prepared by one's self, or be 
bought from the Platinotype Company or their agents, it 
is absolutely necessary for its preservation that it be stored 
in damp-tight calcium tubes. These tubes can be obtained 
directly from the Company, or they can be made by any 
ordinary tinman. They are nothing else but ordinary 
soldered tubes, having at one end a perforated compartment 
containing dry calcium chloride ; this is commonly mixed 
with asbestos, or some fibrous material. The joints of this 
tube are made air-tight by means of a broad indiarubber 
band. We find it an advantage to grease that portion of 
the tube over which the removable end slips ; this not 
only tends to make the joint more air-tight, but it also 
enables the tube to be much more easily opened and 

The calcium chloride itself is best wrapped up in one 
or two thicknesses of muslin ; this prevents any small 
particles finding their way through the perforated diaphragm 
and falling on the paper, which it would at once mark. 
The calcium chloride should be examined from time to 
time, and when found saturated with moisture it should 
either be removed and fresh substituted, or else dried. It 
requires pretty considerable heat to thoroughly dry the 
calcium. This is best done in a thin iron dish over a 
Bunsen burner, the heat being continued till the mixture 
becomes crisp and of a white colour. If asbestos be used 
as a vehicle, the lumps can be heated till they are red hot, 
as it will not bum. On first heating the chloride it will 


appear to become wetter and more flabby; the heating 
should, however, be contmued, till it turns of a white 
colour, and gets hard and crisp. 

Hot-bath platinotype paper should always be stored in 
such a tube both before and after printing, as otherwise 
fiat and granular prints may result. 


We will now assume the paper to be in the printing- 
frame and exposed to the light. We have treated elsewhere 
of the particular kind of negative that is best suited for 
reproduction in platinotype ; we have now rather to deal 
with the quality of the light used, sunlight or dififosed, 
bright or dull. 

We may first note that the same results do not obtain 
with platinum paper as with silver — that is to say, hard 
negatives gain nothing from being printed in sunlight, and 
feeble ones in subdued light do not gain in value, and the 
reason of this will be explained hereafter. 

As a rule, however, we should say, avoid printing in 
sunlight. There is a phenomenon, known as solarization, 
which is very marked and prominent in platinum prints; its 
ultimate result is to cause a granulation of the parts affected, 
and a decided loss in intensity of colour, so that the dark 
shadows become lighter than the surrounding parts. 

This solarization has its equivalent phenomenon in silver 
prints, but in these there is no loss of tone, but the parts 
assume a metallic lustre, whereas in platinotype the print 


assnmes an orangy, granular appearance, very different 
from the rest of the print. 

The actual result of solarization is not easily discoverable. 
In silver prints it is undoubtedly a true revival of metallic 
silver on the face of the print, but it is not quite plain 
whether the same obtains with platinotype, whether it is 
metallic iron being revived, or whether it is a phenomenon, 
like the reversal of the developable silver image, and the 
ferrous salt is partly reconverted back again into the ferric 
stage. The phenomenon is not restricted to the hot-bath 
process, but is equally found in the cold-bath process, 
showing that the platinum salt does not enter into the 
phenomenon. At the same time, in the cold bath the 
ultimate result differs somewhat; instead of the solarized 
part developing lighter, it has a tendency to become darker, 
especially when a weak developing solution is used ; the 
deposit then tends to form into masses of flat, dark shadow, 
granular and devoid of all gradation, giving a somewhat 
curious impasto appearance to the proof. 

As this condition of the provisional image has the power 
of throwing down the ordinary platinic chloride very freely, 
it would seem to favour the hypothesis that the iron is 
reduced completely at these spots. A damp condition of 
the paper tends to accelerate this proneness to solarization, 
which is another argument in favour of using pads. 

In platinotype printing it is not possible to follow the 
progress of the printing like one can in silver printing, but 
a good deal of the image is visibly formed and seen ; in 
colour it is of a purplish tinge, and stands up fairly well 
against the yellow of the surface. 


It is always a difficult matter to describe exax^tly the 
point at which the print should be removed from the 
printing-frame. It is reaUy a matter of education of the 
eye. When accustomed to platinum printing, one can see 
a great deal more detail than one could at first ; in fact, 
some of our best workers assert that they can see everything 
they wish to bring out. Undoubtedly, if at the edges of 
the negative the paper be protected by an opaque mask, so 
that one may have a portion of the paper that one knows 
has not been subjected to exposure to refer to, it is really 
possible to see a great deal of the detaQ. As a rule, one 
should print tiU the detail in the half-tones just shows ; 
for instance, taking a portrait, all the detail m the shadow 
side should show, and the outUnes in the Ughted side, but 
the details in the hair and face on this side should not 
do so. 

As a rule, beginners will be found to considerably over- 
expose their prints ; on development these come out flat, 
and hence the general theory that it requires very hard 
negatives to get good prints. The real cause of this, we 
think, is not an affair of getting out more or less detail, 
but rather an affair of intensity. Workers accustomed to 
the gradual and visible darkening of silver paper cannot 
believe that the faint lilac image on the platinum paper 
can ever give them the deep shadows silver prmting has 
taught them to expect. 

We must, in platinum printing, banish all thought of 
getting density on the print whilst in the frame, and simply 
look to the appearance of the detail ; if this be done, we 
opine that the worker will have no difficulty in rapidly 


obtaining a complete mastery over platinum printing. At 
the same time, it must be remembered that diflferent pre- 
parations of the paper may give results more or less visible 
before development, and we think old platinotype workers 
will bear us out when we say that the present brands of 
paper as sold by the Company give a much more visible 
image than that sold by them some years back. 

Whilst the constant worker in platinotype will, we feel 
sure, find no difficulty in always correctly exposing his 
prints, yet the amateur, with his intermittent printing, may 
not be so successful. To such workers we cannot too highly 
recommend the use of a sensitometer. It is really totally 
immaterial what sort of sensitometer is used ; any paper or 
plate that is divided into squares or parts having different 
opacities or power of resisting light, will do. An excellent 
one can be made on silver or platinotype paper itself. 

Take a slip of sensitized paper, and divide it by pencil 
lines into, say, twenty divisions ; now expose these divisions 
to light in the following ratio : the first one 1 second, the 
second 1^, the third 2, and so on, so that each third division 
has twice the exposure the first had, thus : — 1, li, 2, 3, 4, 6, 
8, 12, 16, 24, 32, 48, 64, 96, 128, are the ratios of the 
exposure. What the actual times of exposure should be, 
depends, of course, on the light ; the longest exposed parts of 
the slip should be so arranged as to get maximum blackness. 
Each division of this slip is, after development, then marked 
with any consecutive figure or letter. Whilst the negative 
to be printed from is being exposed, a slip of paper, cut off 
from the edge of one of the prepared sheets of platinum 
paper, is placed underneath this graduated slip ; the print is 


examined from time to time, and when it is considered to 
be finished, removed from the printing-frame, at the same 
time the trial slip is removed from nnder the graduated 
sensitometer, and the last number visible, without develop^ 
ingy is recorded. 

If, after the print has been developed, it is found to be 
correctly exposed, the number read off under the sensito- 
meter is the key number of the print, and wherever or in 
whatever light the negative be again printed from, it is not 
necessary to examine the print at all, but when the key 
number just shows on the strip under the sensitometer, the 
print is finished. 

Should the first print not be correct the first time, one 
has only to expose fresh prints and fresh slips till higher or 
lower numbers on the sensitometer are brought out, in 
accordance whether the print was found to be over or under 
exposed. By this system of trial and error, the key number 
of each negative will rapidly be fixed on, and, once found, 
should be written on the negative. We feel sure that all 
workers who will take the little extra trouble there is re- 
quired to work thus with a sensitometer, wiU be speedily 
rewarded by the saving they will effect. 

A good deal has been said and written about the rapidity 
of platinum prints. It is generally stated that they are 
three times as rapid as ordinary albumenized silver paper. 
It IS, of course, a matter of extreme difficulty to make any 
expenments in the relative rapidities of the two classes of 
prmts, as ordmary silver paper varies so much in rapidity, 


according not only to variations in its preparation, but also 
according to its age, manner of keeping, etc. 

On the whole, we doubt whether platinum paper has any 
very great advantage over silver paper in good condition,, 
and if the latter be home sensitized and fumed with am- 
monia, it certainly has none ; at least, it will have but 
slight advantage if the light be good, but when we come to 
the yellower light of winter, platinotype has certainly a 
great advantage over silver. The explanation of this is 
to be sought for in the diflferent behaviour of the salts of 
iron and silver under the action of the spectrum. 


After removal from the printing-frame, the proof is to 
be stored in the calcium tube till such time as it may be 
convenient to develop it. This development is normally 
effected by wetting the surface of the print with a hot 
solution (160'' to 180° F.) of neutral oxalate of potash. 

This solution of oxalate is not quite a saturated one, the 
quantities usually given being 130 grains to the ounce ; 
but it rapidly becomes so through evaporation, after being 
heated once or twice. It is, therefore, our practice to com- 
mence with a saturated solution, having always the crystals 
in excess. One reason for this is that there is no danger of 
the oxalate solution becoming spent, as the fresh crystals 
always keep it up to the working point. 

As the development of the print is practically instan- 
taneous — ^that is to say, the greater portion of the platinum 
18 substituted for the iron on the first contact of the oxalate 


— the method usually adopted is to float the sensitized 
surface of the print over the surface of the oxalate solution. 
For this purpose the oxalate is contained in an iron dish 
considerably larger than the print to be developed ; the 
particular kind of dish mostly used is one that is employed 
in cookery, the inside of which is covered with a white 
enamel that is stated to contain no lead in its composition. 

This dish is placed on a gas or other heating apparatus, 

and warmed till it attains a temperature of 180° P. ; this 

is known by keeping in the liquid a small thermometer 

(graduated up to 212° P.) closed in a glass tube. This is 

not a very accurate method of guaging the temperature of 

the bath, as if the thermometer be moved and placed directly 

over the flame, it will indicate a higher reading than if left 

at the side of the dish. However, the exact temperature is 

of no great importance, there being no practical difference 

observable between temperatures of 160° and 180° P. 

Ine prmt is then seized by the two opposite comers, one 
m each hand, and the nearest edge to the operator, the one 
held in the left hand, lowered on to the surface of the 
J^ ' J ^ight hand is then moved away, and lowered at 

^T_ 1. f, ^^^' I^ this way the print can be placed on to 
the liqmd wii^h ^ . . . . , 

? . ^^y- one contmuous sweep. Any stoppage m the 

It is sum • • ^^^^^^^ly cause a line along the line of stoppage* 

a few triak ^^ ^^^ ^^®P^ ^^® ^^ ^^ floating the paper after 

in this mai^^^i^ ^^^ * ^^^^ P®^® ^^ P^P®^ "^^^ ^® ®P^^^ 

A further ad v""- 

way is that it ^^^ge of putting the paper down in this 

the surface of ^^^®® ^^7 bubbles or scum that may be on 

*^tie developer away before it* At timesj 


however, bubbles will be formed. It is advisable, therrfore, 
directly tUe paper has been lowered on to the developer, to 
pick it up again by one end and see whether any bubbles 
have been formed. If so, the bubble should be broken, and 
the print again be lowered on to the liquid, when the place 
protected by it will be developed, and if the bubble be small, 
no trace of its presence wiU be left. But if the bubble be 
large, we have invariably found that a distinct insensible 
line is left, following the outlines of the bubble. 

Time op Development. 

The development of the hot-bath platinotype is almost 
instantaneous, and the image is formed almost directly the 
print is placed on the bath ; at the same time, by leaving it 
on the bath no ill effects are to be apprehended. In practice, 
the print is left on about ten to fifteen seconds. 

Fixing and Washing. 

After removal from the developing dish, the prints are 
immersed in a bath of hydrochloric acid and water (1 in 60), 
and left in here ten minutes ; they should then be trans- 
ferred to a second dish of the same strength, and allowed to 
remain in it about five minutes. After this, they should be 
again passed through a third bath of the same strength. If 
this third bath shows any signs of yellowing, the prints 
should be treated to a f ourtL In all cases, the last bath 
should show no signs of yellow discoloration after the 
prints are immersed in it. 

In practical working, all these baths are not made up 
fresh every day, but used in progressing order — that is to 


say, the first bath of yesterday is thrown away, and the 
second bath of yesterday becomes the first of to-day, and 
so on. 

Economy, however, is not to be sought for at this stage, 
for the only weak and attackable point in a platinum print 
is its liability to discolour in the high lights if iron be left 
in the paper. 

After removal from the last acid bath, the prints require 
about ten minutes* good washing, when they are ready for 
drying, trimming, and mounting. 

Vaeiations in the Temperature of the Developer. 

The temperature of the developer has a somewhat distinct 
influence on the density curve or scale of gradations of the 
print. We mean by this that, supposing the slip of 
graduated paper which we have used as a sensitometer to 
be divided into twenty parts, and by the ordinary develop- 
ment, when No. 1 square showed the least darkening. No. 
10 would then show the most darkening, all the higher 
squares having the same intensity. If we, however, alter 
the temperature of our developer, we should find that, 
although the square that showed the least darkening had 
not altered, yet the No. 10 square, that gave the maximum 
darkness, would no longer do so, but the darkest point 
would be obtained at a higher number. 

Let us examine the practical effect of this. The sensi- 
tometer is in reality nothing but a simplified negative that 
tiontains, howeVer, every gradation from half-tone up to 
deepest shadow. If we take the first ten squares, we shall 


be representing a thin negative, all half-tones and no heavy 
deposits ; but if we include, say, fifteen squares, we shall 
represent a brilliant or hard negative with every gradation 
in it. Now, we see that by varying the temperature of our 
developer we get identical results from both portions of the 
sensitometer. A hot developer will bring the tenth square 
up to maximum blackness, whereas with a cold developer it 
will only be the fifteenth square that attains this desider- 
atum ; therefore, when printing from a thinnish negative, 
the developer should be used as hot as possible, whereas, 
when the negative is hard, the developer should be used 
cold, or nearly so. The converse of this is, that if brilliant 
results are wished for from an ordinary negative, the 
developer should be used very hot, whereas, if soft results 
are to be obtained from the same negative, the development 
should be with a solution at about 80° F. 

We would refer those interested in this question to the 
special chapter on the subject in the Appendix. 

We will recapitulate here the best procedure to follow 
for different kinds of negatives, assuming that a normal 
effect is to be obtained. 

Thin Negative, — Print in the shade or under ground 
glass and give as short an exposure as practicable, and use 
as hot a development as possible. 

Normal Negative. — Give fall exposure, and develop at 
about 160° P. 

Hard^ Dense Negative.* — Give bright light or sunshine 

. * By a hard, dense negatiye we do not mean one that is fogged, but 
only a negative where the high lights are very opaque, whilst the shadows 
are clear glass. 



very fall exposure (snnlight is usefnl) ; develop on a bath 
at 60° to 80° P. N.B.— In this cold development, take 
care that the bath is not in an acid condition, or granu- 
larity may result. The bath may also be advantageously 
diluted with water. 

We leave it to the inteUigence of the reader to fill up the 
gaps between these cardinal divisions. 

Class of Negative Suitable for Platinotypb. 

A good deal has been written anent the peculiar quality 
of negative that is required for platinum printing. It is 
generally stated that what is known as a hard negative is 
an absolute necessity. Now, it is of course very difScult 
to precisely describe what is exactly meant by a hard or soft 
negative, and different workers may have very different 
ideas on the subject. Prom a series of trials that we carried 
out some time ago, we find the density curve of platinum 
paper developed at 160° P., and commercial sensitized 
albumenized paper, to be about the same. This proves 
what practice has shown us, that the negative that gives 
a good, plucky silver print will also give a good, plucky 
platinum one. At the same time, it is more easy to obtain 
a passable print from a thin negative on silver paper than 
it is on platinum. But if the instructions for the treatment 
of a weak negative that we have given above be followed, 
the difference will not be very noticeable. 

In our above remarks we refer, of course, only to platinum 
paper as sold by the Company. We have shown in the 
instructions for preparing the paper how the platinotype 


may be rendered capable of giving hard results from thin 
negatives. The same obtains with silver paper — which is 
assumed to be any good commercial brand ; with a home- 
made silver paper that has been heavily salted, and excited 
on an ammonio-nitrate of silver bath, good results can be 
obtained from extremely thin negatives. 

After-Tebatmbnt of Paper. 

Whilst still in the washing water, platinotype prints have 
a beautiful glossy appearance, but after drying they 
naturally lose this gloss, and dry matt. Although this is 
considered a great advantage by many, yet there are some 
who still prefer the polished surface. Platinum prints can 
be burnished in the ordinary way — that is, a solution of 
Castille soap in alcohol is rubbed over the mounted print, 
which is then passed through any ordinary burnisher. 

Another method, due to Leon Vidal, which will be found 
fully described in the Photographic News^ 1886, p. 829, is 
as follows : — Half an ounce of borax and one dram of 
carbonate of soda are dissolved in ten fluid ounces of boiling 
water; then two ounces of powdered white shellac are 
added, and the boiling continued till the shellac is dissolved. 
Any loss by evaporation is made up, and the liquid filtered 
through charcoal. The point is floated on the warm 
solution and hung up to dry, when it will be found to have 
a slight gloss. 

RBTOUOHma or Spotting Platinotype Prints. 

The platinum deposit being directly on the surface of 
the paper, it is of course an exceedingly easy matter to 


stop-out any imperfections of the print by means of ordinary 
water-colours. This absence of all surface glaze also renders 
the prints particularly available for colouring purposes, as 
washes can be laid over these prints with as great facility 
as on ordinary drawing-paper. The only danger is that 
the print, through a too long sojourn in the acid clearing 
baths, may have lost all its sizing and become porous, in 
which state it would be necessary to re-size it in the ordinary 
way. The colour of the deposit varies from brownish- 
black to black and bluish-black, and therefore the colours 
most useful will be a mixture of sepia, indigo, and 
india ink. 

We need hardly point out to artists the value that the 
platinotype has for all purposes where a photographic basis 
is to be used. All kinds of paper or stuffs can be easily 
prepared according to the formulae given in another part of 
this work, and by the use of suitable negatives, a thin, 
delicate impression, containing every detail, but having no 
intensity, can be obtained, over which the picture may be 
finished either in pastels or water-colours, or, if suitably 
sized, even oil-colours. 

Failures : their Causes and Remedies. 

1. In self -prepared paper, general fog ; otherwise the 
pictures are good. 

a. The paper was affected by light during the sensitizing 
or drying. The remedy is obvious. A slight reduction in 
the platinum print not being observable till after develop- 
ment, particular care should be taken during the preparation 


of the paper, and no reliance be placed, as in ordinary 
silver printing, on the appearance of the paper nnder treat- 

h. Too high a temperature in drying ; this should not 
exceed 104° P. 

c. The ferric solution has gone bad. The ferric-oxalate 
solution, being destroyable by light, should be carefully 
stored in the dark. To test any doubtful solution, add the 
ferri or red cyanide of potassium, when, if any ferrous salt 
be present, it will strike a blue precipitate. If the ferrous 
salts are only slightly present, the red prussiate will restore 
it again. 

2. The prints are weak after development. 

a. Paper has become damp. In this case granularity is 
generally a concomitant of weakness. We have ah'eady 
spoken fully of the remedy. If such paper is not seriously 
affected, something may be done by over-printing, and 
developing on a cold, diluted bath. 

h. The paper is too old. In this case the results are 
characterized both by fog and weakness. 

Mr. Burton gives (British Journal of Photography^ xxxviii. 
p. 421) a method by means of which old or spoilt platinotype 
paper may be made serviceable by adding potassium hypo- 
chlorite or sodium hypobromite to the developing solution. 
He gives no formula. We have found that chloride of 
sodium (table salt), added freely, an ounce or so to the pint, 
kept the whites clear in commercial platinum paper that 
had been left in the damp for over a year. The proof was, 
of course, considerably over-printed. Willis recommends 
potassium chloride as a restrainer. Burton also notes that. 


with fresh paper, the hypobromites and chlorites tend to 
give hard results. 

8. The prints are vigorous, but come out fiat after 

a. Cause : lack of sizing of the paper, whereby images 
sink into the substance of the paper. Remedy : with such 
paper employ more of the gelatine or arrowroot sizing. 

h. The drying of the paper has been too slow. Remedy : 
we have already treated of the precautions to be observed 
in drying ; ten minutes is about the correct time. 

4. The prints on development are vigorous, but the 
platinum black falls off in the developer. 

a. Too rapid drying, causing the iron and platinum salt 
to be formed on the very surface of the paper itself, and 
have no cohesion ; or it may arise from using a paper with 
a hard glaze, and not having sufficient sizing in the sen- 
sitizing solution to enable this to lay hold of the glaze. 
Remedy : see the last failure. 

5. The paper is yellow in the high lights. This may arise 
from several causes. 

a. The sensitizing solution is not acid, and an insoluble 
basic precipitate of iron has been formed in the paper. 
Remedy : follow the instructions more carefully. 

h. Paper that has been blued with ultramarine will turn 
a yellow colour after treatment with iron. Remedy : when 
using an unknown paper, trials should be made to see 
whether the paper suffers when in contact with hot oxalate 
of potash or hydrochloric acid. 

6. The prints after development are too hard. 
a. Too short an exposure. 


h. Too much chlorate m the sensitizing solutions. The 
remedies are obvious. 

7. Spots and streaks : dirty brushes, pads, or fingers. 
Wavy streaks are frequently caused by the surface portions 
of the sensitizing solution being reduced by keeping, or 
having been already used and returned to the stock. Eemedy : 
cleanliness, and use of fresh solution each time. 

8. Black spots. 

a. Minute particles of metal, chiefly brass or iron, in the 
texture of the paper itself ; these set up nuclei, around which 
there is a violent deposit. 

h. The iron is sometimes carried up by the Bunsen burners 
used in drying the paper. 

c. Or such spots may also be due to impurities, or even 
metallic platinum in carelessly prepared chloro-platinite. 

Remedies. — Use a purer sample of paper, and examine 
sheets carefully by transmitted light for minute specks. 

h. Use brass Bunsens, or, better, brush or clean them out 

c Filter the solution. 

If the ready-sensitized paper is bought from the Company, 
it is assumed that no fault will be found in it, and therefore 
all failures are attributable to the subsequent manipulations. 
We have first the obvious faults and their more obvious 
remedies of over and under exposure, the one shown by 
general fog and flatness, the other by great hardness and 
want of detail. 

Granularity may be caused on the best sample of paper 
by damp ; keep it, therefore, scrupulously dry. 

The developer can be used over and over again, but at 


last it will become weakened and saturated with iron salts. 
Indeed, the bottom of the bottle may be full of crystals of 
potassio-ferric oxalate, and still the developer work well. 
Sometimes, however, prints come off the bath weak from 
a spent developer. The developer should therefore always 
have undissolved crystals of oxalate of potash at the bottom, 
and the water evaporated off at each heating can then be 
made up again. Such a developer will keep a very long 
time ; when it gets, however, veiy yellow, it is best to make 
up a fresh one, throwing the old one away. 

Black spots on the prints are sometimes caused by particles 
of iron that fall on the print if it is cut by a steel knife, or 
more often they are particles torn off the calcium tube in 
opening or shutting it. Fold and cut the paper, therefore, 
with a bone or ivory knife, and wrap it up in paper when 
in the tube. 

Spots and streaks, black or white, may be caused by any 
dirt or impurity allowed to fall on the paper. The finger 
will nearly always leave an insensitive mark; the paper 
therefore should be handled as seldom as possible, and never 
touched on the sensitized side. 

The faults that arise from careless development will 
generally take the form of bubbles of a lighter colour than 
the surrounding print, or else form lines with a lighter edge 
across the print. The bubbles have already been referred 
to, and the cause of the lines is a stoppage in lowering the 
print on to the surface of hot oxalate solution. A little 
practice is required to put the paper properly, without 
stopping, in one sweep on the surface of the hot oxalate. 

( 89 ) 



Pboduction of Sepia Tones. 

The natural tone of the paper that we have hitherto 
described is of either a blue-black, or at best a dull black 
without any warmth or richness. By certain additions, 
however, to the sensitizing bath, the image may be produced 
in a fair variety of warm tones, from a warm engraving black 
down to quite a hot sepia. The Platiaotype Company sell 
a special paper which they call their sepia paper, and to 
the special manipulation of this we shall allude in due place. 
We will now proceed to the examination of the formula 
proposed for the production of these warm-toned papers. 

The cause of the warmth is undoubtedly due to the 
presence of mercury in the sensitizing solution, but whether 
the actual colour of the print is due to an amalgam of the 
mercury and platinum, or whether it tends to keep part of 
the platinum in the form of an oxide, or whether the 
mercury may permit of the platinum forming an organic 
salt with the colloid on the paper, is not clear. It is, however, 
certain that the colour of these sepia prints is not so stable 
as that of the black ones, and in the fixing bath they will 


change colour slightly, losing somewhat their sepia tint. The 
change is very slight, and would be absolutely unnoticeable 
in any other process, but a platinotype print is usually such 
an unchangeable thing under every condition, that even 
this slight alteration is remarked. 

The following formula for the production of these sepia 
prints is given by Lainer {Photographiache Correspondem, 
vol. XXX. p. 325) : — 

Chloro-platinite of potassium solution, 1 in 6 6 parts. 

Normal iron solution 2*5 „ 

Normal chlorate solution 8 „ 

Bichloride of mercury, sat. sol. 1-2 „ 

The iron and chlorate solutions are the same as those used 
for the ordinary hot-bath process (see p. 58, ante). 

T. T. Sachers (see Photographic Times^ vol. xxi. p. 489) 
records some experiments made in the direction of obtaining 
sepia paper of a warm tone. He finds that using the 
formula of Pizzighelli, a 10 per cent, addition of a 1 in 20 
mercuric chloride solution to the sensitizing bath, gave a 
rich brown print, having the half-tones of a homogeneous 
colour, and the whites clear. If in addition to this amount 
of mercury added to the sensitizing solution, a further 
amount of about 2 per cent, of the salt be added to the 
developer, the prints will be of a warmer or hotter colour, 
but the half-tones may have a yellowish tinge. 

From the results of his experiments it may be assumed 
that an addition of about ^ grain of the mercuric chloride 
salt per 2 drams of the sensitizing solution is a safe amount, 
although this may be increased for special cases. 


The general manipnlation of the preparations of such 
paper is of course identicaUy the same as in the ordinary 
hot-bath process, and the only fault proper to this process, 
likely to be met with, will be getting a too great quantity 
of the mercury in the sensitizer. This is characterized by 
first the half-tones of the prints assuming a more yellowy 
brown than the deep shadows, followed, if the mercury is 
in excess, by an absolute degradation of the high lights 

Makipulations op the Sepia Paper of the Platino- 

TYPE Company. 

During printing the treatment of this paper differs in no 
way from the ordinary paper, and the same care must be 
exercised, and the printing earned on to the same depth. 
The development can be, and indeed is, carried out by many 
good workers on precisely the same lines as the ordinary 
black paper, that is, using the same baths. The Platinotype 
Company, however, sell a special solution for mixing with 
the ordinary developing bath. The object of this is to 
preserve the whites from degradation. Some workers add a 
small amount of mercuric chloride to the developing bath 
as well, but the results appear to be uncertain. It may be 
noted that the bath used for sepia prints, and especially one 
that has had mercury added to it, should not be used again. 
Several prints may be developed on it in rapid succession, 
but it must not be put aside for another day, and even in 
current use the least sign of degradation in the whites of 
the prints should cause the rejection of the bath. The after- 


manipulations are exactly the same as with the ordinary 

The sepia paper of the Company is an extremely variable 
paper in its colour, but of late it has been much improved 
in that respect, and the later brands of the paper show a 
much truer colour, being, indeed, homogeneous throughout, 
and not, as the old paper did, showing a sometimes decided 
difference in tone between the shadows and the high lights. 
In the Appendix, where we dwell upon what we may term 
the higher development of platinotype prints, we have given 
some special developers for this brand of paper for cases 
where special effects are required. 

After-modifications of Black-toned Platinotype 
Paper in order to get Warmer Colours. 

We have already mentioned that by the addition of 
mercuric chloride to the developing solution, the colour of 
the sepia prints can be altered, and this also holds good 
in the case of the ordinary or black paper. A small 
addition, say about half a grain to the ounce of dry mercuric 
chloride, will generally warm the tone of the print, but 
more than this is a risky proceeding, as frequently the 
double toning, alluded to before, takes place, whilst the 
whites of the prints will also be frequently degraded. 

Another method of altering the colour of platinotypes, 
and one that has been experimented upon by many workers, 
is by means of toning them with other substances, or more 
properly to speak by intensifying them, as the change of 
colour is effected by precipitating on the image some other 



coloured substance. Vogel appears to have been the first 
worker in this direction, although it is true he worked only 
with the idea of intensifying and not altering the colour. 
He describes {Phot Mittheilungm^ 1887, p. 233) how 
he mixed a solution of chloro-platinite of potassium with an 
ordinary dry-plate developer, and flowed the same over a 
feebly printed platinotype. In a short time the solution 
turned black, and metallic platinum was thrown down, and 
attached itself preferably to the existing image on the print. 
The process is interesting, but cannot be regarded as a success, 
although at the same time it is highly probable that, in the 
presence of a reducing agent more under control than the 
one he used, it could be made into a practical process. 

The first worker, however, who produced a practical 
process for toning or intensifying platinotypes was Roland 
Briant (Camera Club Journal, vol. vi. p. 115). Briant 
worked on the lines laid down by Lyonel Clark in his process 
for altering the colour of silver prints toned with platinum 
or other metals by the precipitation thereon of metallic 
silver, from a solution of the nitrate in conjunction with 
acidified gallic acid. Briant gives the following formula : 
About 5 to 10 drops of glacial acetic acid, 1 grain pyro, 
and about 2 drops of a 60-grain-to-the-ounce solution of 
nitrate of silver is made up with water to 1 ounce, and 
poured over the print. The actual proportion of the in- 
gredients varies with the temperature, the idea being just to 
get the silver on the verge of being thrown down or reduced. 
Increase of pyro or silver naturally increases this tendency, 
whilst increase of the acid retards it. If the solution is 
gradually brought up to the right point, the silver will 


begin to first deposit itself on the image already formed, 
leaving the high lights qnite clear, whilst the solution itself 
also remains colourless. The colour of the deposited silver 
is a rich red brown, and the tones given thereby are very 
pleasing. The action is an intensifying one, and tends to 
harden the print, so that flat proofs give the best results. 
Briant experimented with the ordinary hot bath, with prints 
developed with the addition of mercury, and with the 
ordinary sepia paper. He also notes that if required the 
silver image can be again toned with gold, uranium, or any 
other agent, and the colour again be modified, or the print 
may be treated with mercury and again intensified. 

Mr. Fitz-Payne {Camera Club Journal^ voL vi. p. 161) 
carried on independently Briant's experiments with uranium, 
and notes that platinotypes, if they have been carefully 
fixed so as to dissolve out all the iron salts, can be toned 
with the ordinary uranium intensifier to any tone from a 
rich brown to a Bartolozzi red. His formula is as 
follows : — 

A. Glacial acetic acid 1 dram. 

Uranium nitrate 10 grains. 

Water up to 5 ounces. 

B. Ferricyanide of potassium 10 grains. 

Glacial acetic acid 1 dram. 

Water up to 5 ounces. 

Just before using, mix equal parts of A and B, and flow 
over print. The change in colour will take place slowly, 
and when the desired tint is obtained the print is rinsed, 
rather than washed, as the uranium salt dissolves out in 


water, and therefore if intensification has been carried too 
far the print can be reduced by simple washing. 

Strakosch {Photographische CorrespondenZy vol. xx. p. 169) 
gives the following method of obtaining prints of a warm 
colour. In the first place he adds from 1 to 2 parts of a 
4 per cent, solution of mercuric chloride to the developing 
bath. This produces prints having already a brownish 
tone, which are then placed in the following bath : — 

Nitrate of uranium 10 grams. 

Ferricyanide of potassium ... 2 „ 

Glacial acetic acid 60 „ 

Water up to 1 litre. 

In this bath the prints turn of a rich sepia colour, 
getting redder as the toning is continued. When the 
desired colour is obtained, the prints are lightly washed 
in water slightly acidulated with acetic acid, and then 
rinsed in pure water. Strakosch also notes that these 
prints if treated with ferric-chloride assume a green colour. 

It is urged against prints toned or intensified by uranium 
that they are non-permanent, but what is probably a more 
serious objection is the fact that the uranium is practically 
deposited to an equal depth all over the image, and so 
whilst it modifies the half-tones very considerably, the 
dark shadows, where the quantity of platinum present is 
very large, are not modified to anything like the same 
extent, and we get double toning. It is probably for this 
reason that Strakosch first browns his platinotypes with 
mercury, as then the mixture of the red uranium with the 
brown image would be more homogeneous. 


Another method by which the colour of platinotypes can 
be modified is that described by A. W. Dolland {Photographic 
Journal^ 1894, p. 189), and consists in a precipitation on 
the image of metallic gold. From the result of several 
experiments Dolland gives the following bath as acting 
well : — 

Gold terchloride 15 grains. 

Water 74 drams. 

The print is first wetted, and covered, by means of a 
brush or pledget of cotton-wool, with glycerine. When 
evenly covered a little of the gold solution is poured on 
and kept moving so as to touch equally all parts of the 
print. The print will soon begin to increase in strength, 
assuming a blue-black colour, and the action may be 
allowed to continue as long as the whites remain clear. 
When finished the glycerine and gold is washed off the 
print, and the same sponged over with a weak developer, 
the following being a good one : — 

A. Sodium sulphite 1 ounce. 

Metol 50 grains. 

Water up to 10 ounces. 

B. Potassium carbonate 1 ounce. 

Water up to 10 ounces. 

For use, mix equal parts of A and B. The use of this 
developer is to completely reduce to the metallic state any 
gold that may be left in the pores of the paper, which 
otherwise would turn pink on exposure to light. 

Dolland notices that although old prints, that is those kept 


three or four weeks, can be treated in this way, still new 
prints work more easily. 

It should also be noted that the above process is a real 
intensification, and quite faint prints are brought up by it 
to full density ; indeed it has been noticed that detail which 
was apparently invisible in the print was brought to view 
by it. In this respect this process differs from the uranium 
one, which acts more as a stain, and modifies the colour 
considerably without intensifying the print to any great 

The chemical action of DoUand's process is interesting, 
and has given rise to some discussion. Gold in the 
presence of glycerme is certainly thrown down, as DoUand 
showed ; but the action is very slow, and only takes place 
rapidly in the presence of the platinum image. This fact 
has been put down to the platinum, whose power of absorb- 
ing hydrogen is, of course, well known ; but it is doubtful 
whether the real cause is other than physical, being, in fact, 
the same that causes the silver in the experiments of . Clark 
and Briant to only precipitate itself on the already formed 
image. In connection with this point Liesegang, whilst 
repeating the experiments of Clark and Briant {Pkotograjphic 
Work^ 1894, vol. iii. p. 21), noticed that many other 
colouring matters would in the same way preferably attack 
the already formed image, whilst leaving the paper white. 
Amongst others he notes that alkaline pyro, or amidol and 
carbonate of soda, tend to stain a platinotype of a brown 
colour, leaving, however, the whites clear. He also noticed 
the same action with carbon and Woodbury prints, showing 
that in this case, at any rate, the platinum has nothing to 



do with the matter. It woald be interesting to repeat 
DoUand's experiments with carbon and silver prints, and 
see whether gold wonld be deposited thereon in the same 
way as on the platinum ones. 

Extra Rough Platinotype Paper. 

Amongst the papers lately introduced by the Platinotype 
Company is one having an extra rough surface, similar in 
quality to the "rough" surface drawing-paper used by 
artists. Without being altogether a sepia paper, the colour 
of the prints produced on it is of a rich, warm tone, varying 
somewhat, it is true, with different batches, but generally 
tending to greater warmth as the paper becomes old. It 
appears to liave especially good keeping qualities, and we 
have experimented with some that had kept for over a year 
in an open case. Although not in the best of conditions, 
we found that by adding a good amount of common salt 
to the developer, and using the same cold, we got very good 
prints of a warm colour, with the high lights only slightly 

In general use, the treatment of this paper is exactly the 
same as that of the ordinary paper, but it is almost a 
necessity to print with an actinometer, as, owing to .the 
grain, it is extremely difficult to detect the extent to which 
the paper is printed, and the image apparently shows but 
feebly in the frame. Under any conditions it requires a* 
longer exposure than the ordinary paper. Its after-treat- 
ment, also, is the same as that of any other paper, and it is 
amenable to the same variations in development ; but it may 


be noted that it is not successf ally amenable to after-treat- 
ment with a view to altering the colour. 

Paper of this quality is much used by some of our best 
workers, as the grain tends to destroy too prominent detail, 
and at the same time lightens up any large masses of dark 

This paper should be handled with care, even in the tube, 
as if two pieces are allowed to rub together, the pressure 
acting on the tops of the " grain " will frequently cause the 
platinum salt to be reduced, and in the bath these points 
will come up as darkish specks. They are too small to be 
noticeable except under close examination, but they tend 
somewhat to generally reduce the purity of the high lights. 
The same applies to the treatment of the wet print, as the 
surface is very tender and easily abraded, although it is 
probable that when the latest improvements in the 
manufacture of the platinotype paper are brought to bear 
on this brand, this fault will disappear. 


The Company have also of late prepared a large variety 
of linen, silk, and other stuffs, which have been used by some 
workers with success as a basis for ordinary pictures* 
The effect produced is that of a picture on canvas, but 
the prints suffer from the fact that they look as if they 
were copies of paintings, rather than original studies. At 
the same time, in certain conditions and for certain pur-^ 
poses, the regular grain of the material— silk, calico, or 
satin jean, or whatever it may be — ^has a certain value* 


There is nothing that calls for special comment in the treat- 
ment of the stnffs. Of course great care must be exercised 
in the printing to see that the stuff lies flat and does not 
move in the frame when examining it, and therefore it 
is preferable to always work with an actinoiifieter. We 
ourselves, in working on thin silk, have found it useful to 
mount the stuff on a light stretcher, like an artistes canvas 
is mounted, cutting down the back of the printing-frame 
for this purpose. The silk is left on the frame till all the 
manipulations are completely finished, and allowed to dry 
thereon. Development is carried on in the same way, 
but the print should, of course, be immersed bodily in the 
developer, and not floated on it. 

( 101 ) 



This process, introduced by Willis in 1888, was originally 
known as the cold-bath process, but in order to avoid 
confusion with the 1892 process, now also generally termed 
the cold-bath process, we have given it the original designa- 
tion as proposed by Willis himself. 

Although not a commercial process at the present time, it 
having been supplanted by the later 1892 process, which 
produces most of the effects obtainable by it, still it is one 
of very great beauty and simplicity, and it has the advantage 
that the inventor has in this case himself given the formula 
for its preparation. From the SBSthetic point, this process is 
remarkable for the rich velvety brown blacks obtainable by 
it, quite different in their colour from the sepia browns of 
the older process, whilst the fact that the platinum salt, 
instead of being added to the sensitizer, is mixed with the 
developer and brushed, so to speak, on the surface of the 
paper during development, gives a very remarkable brilliancy 
of image. No better distinction between the appearance 
of the results obtained by the old hot-bath and this new 
process can be given than by stating that, whereas the 


former recalled, in its blue-black brilliancy, the idea of a 
steel engraving, the latter, with its rich warm tones, was 
comparable to the best mezzo- or aqua-tint work. 

These warm tones are to some extent obtainable by the 
present processes, but we were so fascinated with the first one 
that it is with regret that we notice its withdrawal. As 
we cannot help thinking that it may again come into use, 
and as its preparation entails no special difficulty, we propose 
to devote a short chapter to it. 

The rationale of this process is the formation of a 
preliminary image in an iron salt, the reduction of this by 
exposure to light, and then the application of a developing 
substance containing the platinum salt, which is then thrown 
down by the reduced iron of the image. This process is 
undoubtedly the natural form that a platinum printing 
process should take, and it is, therefore, not surprising that, 
as Willis states, this was one of his first experiments. The 
difficulty met with, however, was the fact that the provisional 
iron image was dissolved out by the developer before it 
had time to reduce the platinum salt. Willis, however, 
subsequently overcame this fault by adding a substance to 
the provisional image that accelerated the reducing power 
of the iron, whilst at the same time he added another 
ingredient to the developer that retarded its tendency to 
dissolve out the provisional image. These salts were the 
addition of mercuric chloride to the sensitizer, and of a 
phosphate to the developer. 

The preparation of paper for this process differs from 
that for the ordinary process only in the fact that the 
platinum salt is omitted, and from 1 to l\ grains of mercuric 


chloride are added to each ounce of the f erric-oxalate sensitizing 
solution. The paper is coated with this solution in the 
ordinary manner, and a sheet of paper should then have about 
18 grains of ferric oxalate, and ^ grain of mercuric chloride, 
to each square foot of surface. The paper is dried and stored 
in the usual way. The appearance of the surface of the paper 
is of a much lighter tint than the old process, owing to the 
absence of the platinum, being, in fact, of a lemon-yellow 
colour, whilst, during printing, the appearance of the image 
Is less visible than in the hot-bath process ; but this may vary 
with the kind of paper and also with its hygrometric condition, 
the damper the paper the less visible being the image. This 
brand of paper will also be found to print slightly more 
rapidly than the old kind. 

A remarkable feature in this process is the fact that the 
precautions for always keeping the paper dry, so necessary 
in the old hot-bath papers, are here unnecessary, and, indeed, 
for certain effects, the paper has actually to be damped 
before developing. It is, however, not advisable to let the 
paper get damp before printing, although this will not be 
injurious in all cases ; but it is best to store it in the ordinary 
way, and then, after printing, either damp the paper by 
leaving it in a drawer overnight before development, or, what 
is perhaps simpler, by actually steaming it over hot water. 
Willis recommends that the proofs when removed from the 
frames should be stored in flat cardboard deed-boxes. If 
stored in a tin it is advisable to roll the prints sensitized side 
outwards ; this makes the prints more amenable for floating 
on a small amount of developer, and as this contains 
platinum, it is evidently an advantage to use as little as 


possible, and prints curving outwards are of course more 
easily floated than those curving inwards. 

The normal developing solution is made up as follows : 
A mixture of neutral potassic oxalate and mono-potassic 
orthophosphate (termed by the Company the " D " salts, and 
sold ready mixed by them), in the proportion of two of the 
former to one of the latter. Half a pound of these mixed 
salts is dissolved in 50 ounces of warm water. The chloro- 
platinite of potassium is dissolved in the proportion of 60 
grains in 2 ounces of water (this is called the " P " solu- 
tion). (Ordinary water may be used for the D solution, as 
any precipitate will settle when cool, but it is advisable 
to use distilled water for the platinum.) In normal work 
the D solution is diluted by the addition of two parts of 
water to three of D, which gives a strength of about 1 in lOi. 
The actual developer is made up by taking 5 parts of the 
diluted D solution and adding to it 1 part of the P solution. 
This will be about equivalent in round figures to — 

Potassium oxalate 53 grams or 23 grains. 

Mono-potassic orthophosphate 27 „ „ W^ 
Chloro-platinite of potassium 11 „ „ 5 

^^^^ 1 litre „ 1 fl. ounce. 

It will take about 1* to 2 ounces of the above to cover 
the bottom of an ordinary whole-plate dish, but this quantity 
can be reduced by using dishes with plate-glass bottoms. 
Mr. Clark showed a dish of this sort supported on three 
leveUing screws, and having sides of only i inch deep 
by means of which he reduced the quantity of developer 
to about 1 ounce for a 12" x 10" print. The print is 


floated on the developer in the nsnal way, and as the paper 
may be fairly damp at the time of floating, it is an easy 
matter to deal with a thin layer of liquid without making 
bubbles and marks. Directly the whole of the print is 
placed on the liquid it may be at once lifted up and the 
image examined. Its first appearance is of a greyish colour, 
and any masses of shadow may show signs of granularity. 
At this time any bubbles may be broken, and, if small, will 
probably not show. After a few seconds, during which the 
print is held in the hand and watched, it is again placed on 
the bath, to imbibe more of the solution, when it will rapidly 
darken, tending to a warm black, and all the granularity 
in the shadows will disappear. If there is still a want of 
vigour in the shadows, the print may again be placed on 
the bath, by which means the utmost vigour will be obtained. 
The resulting print will be of a rich brown-black colour, 
especially if it should have been damped before developing. 
In the case of small prints, that is up to whole plate, they 
may be developed by means of a brush in which there is no 
metal fastening that can come in contact with the developer. 
The brush must be well filled with liquid, and the strokes 
given with it must be decided and rapid and overlap each 
other, or streaks will show. In the case of landscapes it 
is advisable to commence with the sky portion. 

The brush method is an economical one as regards amount 
of developer, but a little practice is required so as to prevent 
the overlapping of the strokes showing. Above whole plate 
size we cannot recommend the use of the brush, unless, of 
course, tools of a very broad type be used. 

As a general rule it is preferable to use fresh developer 



for each piece of paper, as naturally it takes up after use a 
good amount of the iron salts from the paper, which will 
eventually cause a complete reduction of all the platinum. 
Old developer may, however, be kept for a short time, and 
for certain effects it, with the addition of a little fresh 
platinum, often makes a good developer. Another draw- 
back against the use of the same developer twice, is that a 
scum generally forms on its surface, which comes off on the 
next piece of paper floated, and marks it with wavy dis- 
colorations. This can be remedied by skimming the de- 
veloper after each print has been floated, and in cases where 
several prints are consecutively developed on the same bath 
it is a necessary precaution. 

The further manipulations of this process do not in any 
way differ from those in use in the ordinary hot-bath process, 
and call for no further remarks. 

This process is remarkable from the fact that it gives 
the operator great facilities for producing different effects 
by varying the components of the developer. As regards 
the proportion of the two salts that make up the D solution, 
there is but little to be gained in altering them ; but consider- 
able variations can be effected by altering the strength of 
the D solution, and also its proportion to the P salt. 

By decreasing the quantity of D, the developmg action is 
accelerated, the tones given are colder, and there is a greater 
tendency to granulation, whereas by increasing the quantity 
of D the reverse is the case, whilst at the same time there 
is also a tendency to destroy half-tones, that is, to give a 
shorter scale. 

On the other hand, an increase of P gives increased 


vigour and perhAps richer tones, whilst its deciease gives 
the opposite effect. At the same time, the duration of 
development affects also this variation, and a print if 
floated longer on a solution weak in P will, within limits, 
give as strong an image as if P had been normal. 

Variations in the tone or colour of the resulting prints 
can be obtained by suitable means. The preparation of the 
paper has, as in all the other processes, most to do with this, 
but the colour is also largely affected by the degree of 
dampness of the paper at the time of development. If the 
paper, after printing, be actually steamed until it is quite 
flabby to the feel, and developed in this state, very warm 
tones are obtainable, and it would look as if some organic 
salt were formed between the iron of the image and the 
colloid of the paper, that altered the general character of the 
platinum thrown down. 

Slightly warming the solution increases the strength of 
the platinum deposit, without, however, affecting the colour, 
and it is, therefore, a useful procedure to adopt in the case 
of thin negatives, or where very brilliant effects are 

For normal negatives an old solution, that is, one that has 
already developed a print, can be used, a little fresh platinum 
being added to it for each new print. We have found 
in developing prints 12" X 10", that if about 3 drams 
of new developer be added to that just used, good normal 
results are obtainable. The used solution should not be 
allowed to remain in the dish, but should be poured into 
a bottle from which the clear part can be decanted off when 


Of course, in those cases where a number of prints are to 
be developed at a time, it is simpler to make up a sufficient 
bulk of solution, and float the prints on it in the usual 
manner, one after the other. Care, however, must be taken 
to remove the scum that may form on the surface of the 
liquid ; a slip of paper dragged over the surface, or even a 
good rocking of the dish, being easy methods of attaining 
this end. 

Needless to say that it will always repay to keep any of 
the residues of spent baths, as they will be found to be 
excessively rich in platinum. 

Mercuric chloride may be added to the developer to warm 
the tone, but, owing to the presence of mercury already in 
the paper, it must only be added with the greatest caution. 

In dealing with hard negatives, that is, those having clear 
shadows and opaque high lights, a flattening of the scale 
may be obtained by diluting the normal developer or 
increasing the proportion of the D to the P salt, or, lastly, 
by using an old and enfeebled developer. There is, how- 
ever, always the danger to be apprehended of granularity 
ensuing. We have noticed that the addition of a small 
quantity of the ordinary platinum chloride of commerce 
an effect in lengthening the scale. A suitable 
ii ]f i^Ti ^1^ ^^ niake up a new P solution, containing 

effect, howe^r is T°"*^ ^* chloro-pMinite. A curious 

on a print th t Vi ^^^^ced when the ordinary chloride is used 

of this solarizltior ^^^ ^^^^^zed in places. The appearance 

paper, but it sh ^^ ®^^®what the same as in the hot-bath 

^ ^' a lighter tint on the lemon-yellow 


ground. When a platinous salt is added to the developer 
these solarized parts develop out lighter in tone than the 
surrounding shadows, with a tendency, sometimes strongly 
marked, to mealiness ; but in the presence of a platinic salt 
these portions develop out much blacker, and look as if bold 
washes of Indian ink had been put on the print to emphasize 
the shadows. 

Under-exposed negatives are best treated by slightly 
increasing the quantity of all the salts, and at the same 
time slightly warming the developer ; but, of course, not 
much can be done in the direction of compensating for 
under-exposure, for if a print has not been sufficiently 
exposed to oxidize the iron salts, it stands to reason that no 
alteration in the developer can bring about a reduction of 
the platinum. 

In the case of an over-exposed print, something may be 
done by keeping down the active constituents of the 
developer, so as to have the action well under control, but 
the danger of mealiness is always at hand. The best way 
under these conditions is possibly the addition of some 
other salt that will tend to retard the reduction of the 
platinum. As we have mentioned above, the use of a 
platinic instead of a platinous salt tends this way, but 
probably the addition of potassic chloride, as recommended 
by Willis, will be found more efficacious in the majority of 
cases. We may also mention that we have found that 
sodium-chloride — ^that is, common salt— 'acts very well. 
The action of a chloride appears to be a true restraining 
one, and the image simply takes longer to appear, the scale 
of gradations not being altered in any way^ A convenient 


form of developer for over-exposed prints would be the 
normal developer having added to it about an equal bulk of 
a 10 per cent, solution of potassic chloride ; but the amount 
of chloride present appears to make but little difference to 
the final result. 

Most of the errors likely to be met with in this process, 
and their remedies, will be practically the same as those in 
the hot-bath process ; but there may specially be mentioned 
the tendency to granulation of the image, which is charac- 
teristic of a too short or too feeble development, and the 
formation on the surface of the print of wavy or streaky 
blotches from a scum being formed on the surface of a used 
developer. It may also be mentioned that a general weak- 
ness in the tone of the image will, in this process, generally 
be found to be caused by the amount of platinum salt in the 
developer having for some cause or other fallen considerably 
below the normal, and its remedy is self-evident. 

The appearance of solarization we have already alluded 
to, and when caused by a negative that usually gives good 
platinum prints, may be looked for in the fact that the 
paper was allowed to get damp before printing, or had 
absorbed moisture in the frame. 


cutting inth i ^^^ preparation of blocks for 

in the bath r ^^^ ^^® ^^ ^ undoubtedly this platinum 
solutions here ^^^ ^^?^ ^^^ *^® ^^^^ results, as all the 

applied in as nearly a dry state as is 


possible, and, therefore, the pores of the wood are not 
rendered rotten by prolonged immersion or hot solutions. 
In treating wood, if porous, it should be rubbed over with 
any size, preferably arrowroot, applied in as dry a state as 
possible. The sensitizing solutions should also be applied 
in the same condition, and dried very rapidly. The wood 
should be developed with as little solution as possible, 
applied with cotton-wool, and the unaltered image be 
merely wiped off in the same manner, no fixing with acid 
being necessary in this case. The image will then be 
almost entirely on the surface, and the wood will cut freely 
and not be rotten, nor will the image itself come up as a 
film under the burin. 





This process, which is not to be confounded with the 
platinom-in-the-bath process, is the one which, together 
with the hot-bath process already folly described, is at the 
present time in everyday commercial use. The preparation 
of the paper is, however, as yet a strict secret, and no 
description of any sort has as yet been published. It 
differs from the hot-bath process in the fact that it can 
be developed at the normal temperature of the room. It 
is true that this can also be done with the hot-bath process, 
but only as tour de force^ and after taking certain precau- 
tions, whereas the present process is most successfully 
worked under these conditions. As we know from the 1888 
process, cold development requires increased insolubility 
of the sensitive coating, and in the present process the 
insolubility obtained is very remarkable ; so much so that 
prints can be developed in patches, without the lines of 
demarcation showing, whilst bubble marks are unknown. 
In the 1888 process, insolubility of the coating was obtained 
by the addition of mercmic chloride to the sensitiser and 


a phosphate to the developer. In the present process, how- 
ever, as ordinary oxalate may be used as a developer, the 
improvement must he sought for in the sensitive coating 
alone. It may be possible that it is obtained by the use 
of the bichromates or chrome alum, or some substance 
tending to make the exposed portions of the image in- 
soluble to a more or less extent. We say to a more or less 
extent, because the coating of this paper is not in any way 
completely insoluble ; that is to say, if the print be placed 
in water, nearly all the surface will be dissolved oflF, and 
on the application of the developer only a feeble image of 
a brownish colour will appear. It may also be noted that 
the insolubility increases with age ; that is to say, paper that 
has been kept for some months, even in an hermetically 
sealed tube, is more insoluble when old than when new, and 
paper left overnight in an open drawer will also be found to 
become more insoluble than paper fresh from the tube. 
Such behaviour, it may be remarked, is not inconsistent 
with the presence of a bichromate, and it may be noted 
that Professor Lainer, who has experimented a good deal 
with platinum, gives, in the Photographische Correspondez 
(see Photographic News^ 1894, vol. xxxviii. p. 120), the 
following formula containing bichromate of ammonium for 
the preparation of platinotype paper suitable for cold 
development : — 

Solution No, 1. 

Ammonium ferric oxalate . . 

.. 50 grams. 

Distilled water 

50 c.c. 

Oxalic acid, 10 per cent. sol. 


15 „ 



Solution No, 2. 

Chloro-platinite of potassium ... 1 part. 
Distilled water 5 parts. 

For each sheet of paper mix 8 c.c. of sol. No. 2 with 4 c.c. 
of No. 1, and 8 c.c. of a 1 in 25 sol. of bichromate of 

Lainer notes, however, that — as indeed is to be expected — 
the addition of the bichromate reduces the sensitiveness of 
the paper, and it is not therefore quite proved that a bi- 
chromate enters into the composition of this process. 

Beyond the advantage of dispensing with the hot 

developing solutions, this cold-bath paper has another 

advantage, and that is in the hardness of its sensitive 

coating, which may indeed be rubbed with considerable 

vigour without injury. This fact gives us a valuable and 

useful means of mechanically restraining or retarding the 

development by the aid of glycerine. To this end the 

glycerine is actually rubbed, by means of a bit of flannel 

or pledget of cotton-wool, all over the surface of the picture, 

or, if preferred, merely over those portions that it may be 

desired to keep back. The effect of glycerine so applied 

IS very remarkable, in the complete immunity it gives from 

any marks caused by bubbles or stoppage of the developer, 

and consequently gives us a very great faciUty for modify- 

S e am portions of the print. For instance, the shadows 

. , , ®^^y foreground may be kept back by glycerining 

furthe • r? •? ^^^^^ fi^*'> ^^^ *^^^ applying a developer still 

of devel ^ ^^ with glycerine, by which means the time 

_ ^ut nxay be made to extend over several minutes, 


daring which time any of the less-exposed portions of the 
view can be brought up to f nil density by the local appli- 
cation of a fresh, strong, or undiluted developer, and that 
without the slightest danger of the lines of demarcation 
showing. In the same way vignetting may be most suc- 
cessfully accomplished, as, if the print be well glycerined 
first, the softest effect in shading off may be obtained by 
successive washes of developer, getting stronger and stronger, 
whilst the soft outlines of these washes merge into each 
other and the white of the background, and allow a vignette 
to be developed up out of a proof printed in an open frame. 
When we add, also, that this paper appears to keep better 
than the ordinary hot-bath, and indeed for the first month 
after manufacture actually improves, and when we find that, 
by a suitable choice of developer, considerable variations in 
the resulting prints may be obtained, it can be understood 
how it is that this process has supplanted the old cold-bath 
process, and, indeed, seems likely eventually to supplant 
also its only other rival, namely, the hot-bath process. 

Practical Working of the Process. 

The preliminary operations in this process are exactly the 
same as those followed in the hot-bath process. The paper, 
when removed from the hermetically sealed tubes in which 
it is now sold, should be at once placed in a calcium tube, 
although it is not so necessary that it should at all times 
be protected from damp ; indeed, for certain effects, it may 
be purposely exposed to moisture. 

In appearance this paper is perhaps slightly more yellow 


and less orange in tone than the hot-bath paper, bnt the 

colour of the image formed by exposure is the same faint 

purple. The depth to which printing is to be carried on 

ia naturally a difficult matter to describe in words, but it 

may be said generally that the image is slightly more 

visible in this process, and therefore printing should be 

carried on more fully ; but this is compensated for by the 

fact that it is undoubtedly slightly more rapid than the old 

process. It may also be pointed out that, since development 

is thoroughly under control, there is but little fear of losing 

a print through moderate over-exposure, and therefore, if 

an error is to be made, it should be in this direction. 

There appears to be but little difference lin the results 

between prints developed inmiediately after being taken 

from the frame, and those which have been kept a week 

or two, providing, of course, that they have been kept in 

a proper calcium tube. On the other hand, for certain 

effects, the print may certainly be kept with advantage in 

an open drawer over-night, but a prolonged sojourn in a 

moist place tends to great flatness and discoloration of the 

high lights ; but on the whole, however, we believe that 

the best procedure is to keep the prints, an hour or two 

before development, in an ordinary drawer or box. It is 

difficult to say absolutely that good does always result 

therefrom ; but, generally speaking, this treatment will tend 

to give prints of a warmer tone, whilst, as we have already 

mentioned, there is probably also an increase in their 

There are two ways of developing this paper. The 
first way is to float it on a bath containmg the developing 


solution at the nonnal temperature of the room, in a manner 
similar to that employed in the hot-bath process. The 
second is to lay the print face upwards on a table or piece 
of glass, and brush the developer over it. Both methods 
have their uses. Where the prints are straightforward and 
require no dodging, it is undoubtedly the best procedure 
to float them on the solution, as the brushing on of the 
developer does very often leave marks in spite of the 
insolubility of the surface. Mr. Willis himself certainly 
showed wonderful dexterity in developing paper bit by bit, 
splashing on the developer here and there, and yet turniug 
out prints without markings, but such tricks are not easy 
to repeat every time. Bubbles or small marks may not 
show, but where there are masses of dark shadows, a certain 
amount of platinum black is dissolved off in the developer, 
and is apt to run over the whites and so discolour them. 
At least this has been our experience with most batches of 
this paper, and it is for this reason that we recommend 
floating as a rule for ordinary work. At the same time^ 
floating has the drawback that a scum is apt to form on 
the surface of the bath, which leaves marble-Uke markings 
on the print ; but this can always be avoided by skimming 
the developer. 

In the case, however, of special prints or work that has 
to be dodged, or where but one print is to be treated, and 
it is desired to economize developer, the brushing-on method 
is most useful. But in this case the face of the print 
should always be well glycerined first, which will entirely 
stop any markings from showing. Considerable friction 
can be used in rubbing on the glycerine without any danger 


of removing the surface, aaid, indeed, it can be pat on 
anyhow and in any rongh-and-ready manner. 

The print so treated is then laid, face side upwards, on 
a sheet of glass or even American cloth, and it is not a bad 
dodge to slightly glycerine also in places the surface of the 
glass, as it prevents the paper from slipping. The developer 
is then applied to the print in almost any way. Perhaps, 
for straightforward prints, a tuft of cotton-wool, dipped in 
a normal developer, is the simplest ; but the brush, or even 
the fingers, may be used. Supposing the print to be cor- 
rectly exposed, the image will at once appear, of a greyish 
colour in the first place, but rapidly takes a good black as 
the developer acts. If the action flag, it can always be 
accelerated by the addition of a little fresh developer. If 
over-exposure be feared, or if it is required to " bring up " 
more of one portion than another, then the normal developer 
should be diluted with an equal bulk of glycerine ; or, if it 
is desired to have it very much under control, with equal 
bulks of both water and glycerine. This mixture is applied 
in the way above mentioned, when the image will come out 
much more slowly than before. The moment details reveal 
themselves, some fresh and stronger developer is taken, 
preferably in a brush, and painted on to those parts that 
are to be brought up most. Parts so treated will at once 
attain maximum density, and the stronger developer can 
then be applied to the other parts at will. In treating a 
vignette, for instance, the developer would first be applied 
to the head only, and then this strengthened up gradually, 
whilst the background is brought out as required. 

A stiff hog-hair brush produces a good effect, as it enables 


all the appearance of a brushed-in background to be 
introduced ; the glycerine makes each successive wash per- 
fectly blend with the next ones, and no line of demarcation 
of any sort, not even against the pure white of the paper, 
can be detected. 

Whatever the nature of the print, the moment develop- 
ment is complete to the worker's satisfaction, it is placed 
face downwards in a bath of weak hydrochloric acid and 
water, and the remainder of the operations are exactly the 
same as in the case of the hot-bath process, and call for no 
further comment here. 

We have hitherto spoken of the developer generally, as 
there are two formulae in common use in this process. The 
first is the old hot-bath developer, that is 130 grains of 
neutral oxalate of potash to the ounce of water ; and the 
second the " D " salts abeady alluded to, and whose com- 
position is given on p. 104, ante. We find, however, 
from the results of pretty careful experiments, that there is 
^p appreciable difference between prints developed on these 
bunted developers, or on the same in a condition of satura- 
^^^> and as it is far easier to prepare and keep saturated 
^utions, we strongly recommend their use in both cases. 
^^ developers are used cold, that is, at the normal 
^P^T&tuTe of the room. 
^i^^^hough either developer can be used, still there is a 
^1 ^^Qt diflfe^^iice between the results obtained by them 
^ . "^ both B,TB used normally. The oxalate invariably gives 
^% ^^er-^^^^^ print than the " D " salts, with the shadows 
%^ ^^i; CfJ^^ " D " salts, on the other hand, give a very 
iw^^^ -^^deed, with most intense blacks — blacks 


Which, indeed, only reflect as little as 4 per cent, of the 


These, then, are the general characteristics of the two 
developers when used normally, but in a paper read before 
the Camera Club (see Cam. Club Journal, No. 72, p. 119)» 
Mr. Willis gave a list of certain modifications of or addi- 
tions to them, by means of which certain effects might be 
produced. We have experhnented with nearly all these 
combinations, and we recapitulate here our deductions 

Our first set of experiments were in the direction of 
altering the colour of the prints ; that is to say, we tried to 
get the print of a more or less warm tone. We have already 
pointed out that the oxalate developer is the most favour- 
able for this, and the more so if the print be not very dry 
before development. Willis proposed sugar, starch, gum, 
and such products, as tending to the same end. We have 
experimented with most of these, but we fail to find any 
appreciable effect. We have also tried the addition of 
mercuric bichloride to the developer. We have already 
alluded to the action of this salt on p. 90, and it is very 
much the same here. When added in quantities not exceed- 
ing half a grain to the ounce of developer, it slightly warms 
up the tone ; but it must be used most circumspectly, or 
double toning will result. 

We have also experimented with both developers used at 
different temperatures, but beyond the fact that the " D " 
salts were always about 2 per cent, behind the oxalate in tie 

uTtft Tl' ^'"'"' '^^''- behaviour was otherwise 
similar. AVe found that the general effect of heating the 


developer was to give a less steep curve, and should there- 
fore be used in cases of under-exposure, or when too 
vigorous prints are to be feared. The addition of glycerine 
to these hot developers had the effect of still more accen- 
tuating their characteristics. It may also be mentioned that, 
although there is no difference between the behaviour of a 
saturated and normal developer when used cold, when 
heated the strong developer will not give the same depth of 
colour in the shadows that the cold one will. 

We have also experimented on the influence of acids and 
alkalis on the developer, but found no measurable results. 
If, however, the oxalate developer be very alkaline, it may 
cause a red discoloration of the print ; but, unlike the hot- 
bath paper, it really does not appear to matter much whether 
the developer is acid or alkaline, providing, of course, the 
acidity or alkalinity be not in excess. 

Another interesting series of experiments we undertook 
was that showing the effect of different degrees of dilution 
of the normal developer. We have already pointed out 
that there is no appreciable difference between the normal 
and saturated baths, and very much the same obtains when 
the dilution is carried as far as an addition of six times as 
much water. Development is slower, but nothing more. 
If the dilution, however, be carried on beyond this point, 
there is always a danger of the image being dissolved off. 
If glycerine is used instead of water, this is not the case, 
and the developer may be diluted to almost any extent. 
Super-dilution of the developer may, however, sometimes be 
made of practical use. Suppose the case of a negative giving 
naturally a vigorous print, but from which it was required 


to get a delicate and soft effect. By taking a very dilute 
developer, say four parts water, four parts glycerine, and 
one part strong developer, and, after first glycerining the 
print, dipping a piece of flannel in this developer and, 
wringing it out almost dry, and then rubbing over lightly 
the surface of the print with it, a very delicate image, 
having no heavy shadows at all, but still showing all detail, 
will be developed up. 

There is, however, another direction in which we desire 
control over our prints, and that is in the direction of 
compensation for over-exposure. Several salts have been 
proposed for this purpose ; for instance, the chlorides were 
stated to have a good retarding effect, but with this kind 
of paper we have not found this to be the case. The 
chlorates, it is true, have such an action, but it is far inferior 
to that of potassium nitrite, the action of which as a 
restrainer is very remarkable. When added in the propor- 
tion of one-tenth of a grain to the ounce of developer, it 
shortens the scale most considerably, and when increased 
beyond this the curve becomes almost a vertical line, but 
at the same time the blacks become very enfeebled. As 
compensation for over-exposure, or for brightening up prints 
from thin negatives, probably about one-thirtieth of a grain 
of the nitrite will be found most generally useful. Its effect, 
however, on the developer is transient, and fresh should be 
added as fresh prints are treated. The diagram shows 
the result of exposing four pieces of the same paper for 
varying times to the action of light, and developing with 
different developers. The curves give the light reflected 
after development at 60° Pahr., at 170° Fahr., and when 


one-tenth and one-hondiedth of a grain of uittite are added 
to the cold developer. The effect of the nitrite, as will be 
seen, is veiy marked. 

Lastly, we have tried a few esperimenta on the results 
obtained by printing throogh coloured glasses. Here, 


contrary to what Willis states, we find that coloor makes no 
difference to the results whatever ; and indeed, on looking at 
the ^cale of sensitiveness of the iron salts to the spectrum, 
there is no reason why it should. Of course we were 
working with clear, colourless negatives. If these were in 
any way stained, especially yellow, the result then under 
different-coloured glasses might very well be different. 

( 125 ) 



In this process, which was discovered by Captain Pizzighelli, 
and described by him first in the Thot MUthdlungen (trans, 
by Gunther, Vhotogrcvphk News^ 1887, p. 124, and Photo- 
graphic Journal^ 1887, p. 17), a visible image in platinnm 
black is formed during exposure in the printing-frame, just 
as in an ordinary sUv'r ^nt. and there I no Ir Weiop- 
ment required, as in the ordinary platinum processes, but the 
unaltered sensitized medium on the paper has merely to be 
dissolved off by a bath of weak hydrochloric acid, and the 
picture is complete. On the face of it, this process should 
be a very valuable one, as, by reason of its simplicity, per- 
manency, and visibility of the printed image, its manipula- 
tions should be of the simplest, and when first introduced, 
it leapt at once into favour, and was put commercially on 
the market. Unforfcunately, however, there was always 
a great want of certainty in the quality of the results 
obtained on this paper, at least with the first samples sold, 
and although of late it has somewhat improved, its present 
use is by no means general, and confined, we are afraid. 


mostly to those workers who want the easiest rather than 
the best process. 

The rationale of the process, and at once the cause both of 
its success and failure, is the fact first pointed oat by 
Pizzighelli, that by the addition of a suitable developing 
salt to the sensitizing solution, the iron salt as it is itself 
deoxidized reduces also the platinum salt. But it must be 
remembered that this is only the case when moisture is also 
present in the print. The quantity required, it is true, is 
very slight, but still it must be there, and this fact alone 
makes the success of the paper depend on its hygrometric 
condition. For this reason, in the earlier formulae it was 
recommended to add glycerine to the sensitizing solution, 
although this was soon found to be unsuitable and uncertain. 
It is true that, after a somewhat feeble image has been 
produced in the printing-frame, this may sometimes be 
darkened and rendered more vigorous by after-damping the 
paper, breathing on it or steaming it, and it has also been 
recommended to develop it on a solution of carbonate of 
soda. The samples of paper in the market we have always 
found to vary very much, and it is therefore difficult to 
make any very accurate statements ; but from experiments we 
have made, we have found no beneficial results whatever 
from developing either on soda carbonate or oxalate of 
potash. In no cases did the developer produce any better 
effect than the simple damping, and even this latter, we may 
add, in many cases had not the slightest influence on the 
character of the printed-out image. Cembrano probably 
gives the true explanation of this when he states that paper 
exposed and printed quite dry improves by after-damping, 


but if the paper be expoBed damp no improvement is in any 
case effected by further damping. 

But there is also another reason which must always 
militate against printing out in platinum, and that is the 
opacity of the platinum image formed, which protects the 
unaltered salts below it from further light influence, and 
prevents, unless the exposure be very much prolonged, any 
further visible reduction, thus making the obtention of 
vigorous prints a difficult affair. 

At the same time, however, sometimes very excellent 
results are shown on this kind of paper, and as it is essen- 
tially an easy process, and the paper itself can easily be 
prepared by the amateur, we propose to devote a short space 
to its preparation and manipulations. 

In the first place it is, we think, most essential, in order 
to get good results, that the paper be freshly prepared, as 
even when kept in a hermetically sealed tube it is very apt 
to deteriorate. Old paper, however stored, should invariably 
be exposed to the moisture of the atmosphere for some little 
time before printing, as using the paper quite dry, and 
relying on it absorbing sufficient moisture after printing to 
bring out the image, although sometimes successful, is 
generally very unreliable, and produces many failures, added 
to which paper printed dry gives weak images, and does not 
allow the appearance of the image being followed during 
exposure. Whilst printing in dry weather, however, the 
growth of the image may sometimes be improved by 
breathing on it whilst still in the frame ; but it is evident 
that this can only be successfully applied to the whole 
surface by using a frame having the back in three instead 


of the ugual two divisions. Local parts, however, may often 
be mach improved bj breathing on them in this manner. 

The most suitable negatives for this process are dense 
ones, that is, those having a heavy deposit, with clear 
shadows, and no fog ; or, conversely, with normal nega- 
tives the process will give a low-toned, soft proof. It 
is best to print in a very bright light, indeed sunlight is 
very often the only one that will give good results, and even 
under these conditions the printing is a long affair, as the 
paper is very slow indeed. We have in some cases, where 
we have been endeavouring to get brilliant results, found 
that the ordinary hot-bath paper exposed alongside for the 
same time also printed itself out equally well. With the 
later improvements, however, the rapidity of the paper has 
certainly been increased ; but at its best it must still be 
regarded as a decidedly slow process. 

Printing is carried on in the frame to exactly the depth 
required, as there is no after-loss in the fixing baths ; but 
the print will sometimes slightly change colour, and lose its 
blue-black appearance, becoming slightly duller in tone, 
although not in intensity. 

The fixing of these prints is the same as in the ordinary 
process, and the after-washing and treatment are also in 
every way similar. 

^The finiahed image is, Uke the hot-bath and the other 

processes of WilUs generally, in metaUic platinum, and is, of 
course, as nPTT^^^ i. ., ^ -^ 

manner J^T "", **^^' "^^ P'i^*« ^^'''^ ^^ *« 

ways already d«^^?*'°''^'^ """^ ^""^ ^ *°y °^ ^^' 
bath process! "^ '"^ * previous chapter for the hot- 


As the best results are undoubtedly obtained on paper 
that has been quite freshly prepared, and as the preparation 
presents no difficulty whatever, and can be easily carried out, 
we append a few of the most successful formulae for its 

Preparation of the Paper. 

Any paper that is suitable for the hot-bath process is 
suitable for this one also, and therefore the chapter dealing 
with that subject may be consulted again. 

As we have mentioned above, the speciality of this 
process consists in the fact that the developing agent is 
added to the sensitizing mixture, and in Pizzighelli's 
original description he gives three ways of doing this. In 
the first one, the paper is first sized, and then the developer 
and sensitizer are bitished on in one operation ; in the second, 
the developer is added to the sizing mixture, and the paper 
then sensitized ; and in the third, the whole of the 
ingredients are mixed, and the paper coated in one operation. 

We have no hesitation in saying that the first operation 
will generally be found to be the best and simplest. A 
coating mixture that contains no sticky size, is more easily 
and evenly brushed on the paper, and dries as rapidly as is 
required, whilst the preliminary sizing is always an easy 
operation, and, indeed, with some papers, will be found to 
be unnecessary. 

As sizes, Pizzighelli recommends gum arable, starch, and 
arrowroot, in our opinion the latter being the best, and the 
gum the worst, as coating is often very difficult on account 


of its stickiness. There is also a difficulty in getting the 
gum caref uUy powdered and dissolved, and every care has 
to be taken to see that no lumps, however small, are left, 
as otherwise they wUl cause streaks and spots. 

When arrowroot is used to size the paper in the first place, 
it should be made pretty strong, about one grain to the dram 
is a good bath. Even ^hen used with the sensitizing 
solution, however, it should be about the same strength, 
depending, of course, on the hardness of the paper, and extent 
of previous sizing. Gelatine is unsuitable as a size, as it is 
coagulated by the platinum ; therefore papers that have been 
sized origmally with gelatine should be used with great 
caution, and, if they must be used, it is well to add arrowroot 
to the sensitive coating, and make it more like an emulsion 
on the surface of, and distinct from, the paper itself. 

The original sensitizing formula of Pizzighelli was com- 
posed of ferric oxalate, neutral ammonium or sodium oxalate, 
and chloro-platinite of potassium ; but in his later and 
improved process (see Fhotographic News, 1892, p. 293), he 
recommends the use of ammonio-f erric oxalate and potassium 
oxalate as giving a more sensitive and brilliant paper. 
The following is his latest formula :— 

A. Chloro-platinite of potassium 10 grams or 150 grs. 
DistiUed water 60 „ 2 fl. oz. 

B. Ammonio-f erric oxalate ... 40 grams „ 600 grs. 
Potassium oxalate, 5 % solution 100 „ 3* oz. 
^^y<^^^ ... 8 „ „ 1 dr. 

Heat the oxalate to about 40° C, and then add the 
fernc salt, and filter. The solution will keep in the 


dark, especially if a drop of carbolic acid be added to 
prevent the growth of mildew. 

C. B solution 100 or 8i oz. 

Chlorate of potash, 5 % solution 8 „ „ \ oz. 

D. Mercuric chloride „ 20 grams,, 300 grs. 
Potassium oxalate „ 40 „ „ 600 „ 
Glycerine 2 „ „ |dr. 

For prints of a black or blue-black colour take — 

A. 5 or 77 fl. grains or 84 minims. 

B. 6 „ „ 92 „ „ 100 „ 
C 2 „ „ 30 „ „ 34 „ 

The above, making 13 or 3^ drams, should give 
iabout enough of the mixture to cover a sheet of paper 
26 X 20 inches. 

The chlorate of potash solution C plays here the same 
role as in the ordinary hot-bath process, that is to say, for 
hard 'negatives its quantity should be reduced, and for 
soft negatives, of course, increased. 

The D, or mercuric chloride solution is for the purpose 
of obtaining prints of a warm brown tone, and the follow- 
ing may be taken as an average formula, which may be 
altered slightly in either direction to suit particular 
cases : — 

A. 5 or 1| dram« 
^* ^ »> )> 1 >j 

^' 4 „ ,,1 „ 

The amount of chlorate of potash may, of course, be 


also varied in this fonnida to suit the negative or desired 

It will be noted that in the above formula the use of 
glycerine is advocated in order to provide a hygroscopic 
substance that will keep the paper to the proper degree of 
moisture ; but we think that its use in our damp climate, 
if not entirely suspended, should only be undertaken with 
great caution and in the driest weather. 

For the coating and drying of the paper, we can only 
refer readers to the method described for the hot-bath 

Pizzighelh's process has been considerably worked in 
Germany and Austria, and sometimes with very fair success, 
and we append, therefore, a few further formulae of some 
of the best-known workers. 

Wischeropp {Photographic News^ 1891, p. 39) gives the 
following simplification of Pizzighelli's formula :-^ 

A. Sodio-ferric oxalate* 40 grams or 600 grs. 

Sodium oxalate neutral, 3 % solution 100 „ 3i fl. ozs. 
Potassium chlorate 1 gram „ 15 grs. 

B. Distilled water 60 „ 2fl. ozs. 

Chloro-platinite of potassium ... 10 grams „ 150 grs. 

Mix 8 of A, 5 of B, for each sheet of paper 
26 X 20 inches. 

To obtain warm tones, chloride of mercury may be added 
to the above. A normal formula would be about ^ of 

* Sodio-ferric oxalate, suitable for tMa process, can be obtained in the 
form of apple-green crystals from the Platinotype Company. This salt is, 
t)f conrse, sensitiye to light, and should be kept in the dark^ 


a gram of the salt to each 13 of the mixture given 

Krause recommends, and with reason, the rapid drying 
of paper coated with any of the above formulae, and uses 
a little tin oven, warmed by means of a spirit-lamp, for 
the purpose. Rapid drying, in order to obtain brilliant 
effects, is as essential in this process as in the ordinary 
hot-bath one, and, therefore, our previous remarks on the 
subject should be re-read here. 

The preparation of printing-out papers does not seem 
to have been much practised in this country, and but few 
workers have recorded their experiments. Mr. Cembrano 
(see Camera Club Journal^ vol. ii. p. 155) publishes the 
following experiments : He notes that the potassic- gave 
him better results than the sodic-oxalate. His best results 
were obtained by using Pizzighelli's third formula, where 
the gum arabic was mixed with the sensitizing solution ; 
but he agrees that it is generally best to employ paper 
that is already sized. The following is the formula success- 
fully used by this gentleman : — 

A. Potassium chloro-platinite 

. . . 1 in 8 solution. 

B. Sodio-oxalate, 3 % solution 

... 8 drams. 

Sodio-ferric oxalate 

o „ 

Gum arabic 

2 „ 

Warm the oxalate and dissolve the iron therein, then 
add the gum, dissolve well, and then strain. 

C. Solutions 2 drams. 

Pot. chlorate, 5 % solution ... 10 minims. 


To sensitize a sheet 26 X 20 inches take — 


• • • 

• ■ V 

... 90 minims. 


• • • 

• • • 

• . • oO ^9 


• • • 

• •• 

2 „ 

Cembrane notes the slow printing qualities of this paper, 
and tried to improve it in various ways. He notices a 
slight acceleration dne to the addition of a hygroscopic 
substance such as calcium chloride ; the actual amount he 
found best was an addition of 4 grains to each sheet 
of paper coated. Mr. Wellington, in the same journal, men- 
tions that he had obtained good results by adding sugar 
to the gum solution, and it is quite probable that this 
may be found to be a useful addition, tending perhaps 
to improve the tone or colour of the image. 

( 135 ) 



Although, generally speaking, there is no diiference in the 
chemical action that takes place when a silver salt is used 
instead of an iron one for the formation of a preliminary 
image to be replaced by platinum, still, in photographic 
parlance, a distinction is made, and the term *^ platinum 
toning " is used to denote the process whereby a preliminary 
image, printed ont or developed, is first obtained in silver 
and then the silver of this image is by an after-operation 
replaced to a more or less extent by platinum. 

Many varied formulsB for platinum toning are to be 
found, but as they are all only modifications of the original 
process of Mr. Lyonel Clark, we shall proceed first to 
describe this process, adding to it any modifications of later 
date that we have found useful. 

Platinum toning is applicable, with certain modifications, 
to probably every silver printing process that exists, but 
the best results are perhaps obtained on matt surface 
chloride of silver paper, in which the silver is present 
in large quantity so as to give a vigorous image. 

Such paper is now a common article of commerce, or 


can be easily prepared. The most suitable negatives are 
plucky ones with full gradation, and the paper should be 
printed out until the highest lights are slightly degraded, 
and the darkest shadows should be distinctly solarized or 
bronzed. Paper may be toned at once or kept before toning. 
It should preferably be washed in several changes of water 
before toning, until the milkiness caused by free chloride of 
silver ceases. Paper can, however, be toned without wash- 
ing, but the chloride carried over soon dirties and destroys 
the toning bath. The f ollowmg bath will tone prints very 
rapidly, that is, in a few seconds, the red colour of the print 
rapidly giving way to platinum black : — 

A, Stock Solntwn. 

Chloro-platinite of potassium ... 60 grains. 
Distilled water up to 2 fl. ounces. 

Toning bath : 1 dram of stock solution A, made up 
with water to 2 fi. ounces, to which is added 2 or 3 drops 
of nitric acid. 

In cold weather, or if prints tone slowly, this bath may be 

slightly warmed. A simple way is to float the prints on 

this bath one at a time, and pick them up and examine them 

in the hand. They should be refloated, if necessary, until all 

trace of reddishness, viewed by transmitted light, disappears. 

The resulting colour will then be of a rich purple-black or 

pure black, depending on the original tone of the print ; 

for instance, auunonio-nitrate prints will give, if vigorous, 

^^^y ^^^J^^^^^s, whereas ordinary chloride paper, if red 

when placed in the platinum, will turn a plum-black, or, if 


the image be thin, of a greyish-black colour. The prints 
being wet when placed on the bath, no bnbbles or marks are 
to be apprehended, and, if preferred, prints may very well 
be toned with a brush or pledget of cotton-wool. 

Warmer tones, that is, those having a brownish-black 
tendency, may be produced by diluting the above bath with 
four or five times its bulk of water. The effect of this is 
to keep the toning action undericontrol, and it can, therefore, 
be stopped whilst there is still some of the silver salt left 
unconverted, which, mining with the platinum black, gives 
a warmer tone to the image. 

Fixing is done in the usual manner, but owing to the 
fact that the toning bath is in acid state, it is advisable, in 
order to prevent sulphur being thrown down in the fixing 
bath, and sulphur toning of the print setting in, to wash 
the prints, before placing them in the hypo, in water, or a 
b^th of water rendered slightly alkaline may be used. The 
subsequent washing of the prints in order to free them of 
all hypo, has to be carried out as thoroughly as in the case 
of a gold-toned print, 

Clark notes that no difference in the gradation of the 
image is effected by altering the strength of the toning 
bath, that is, a hard print will always be a hard print, or 
vice verstty whatever the dilution of the bath, within limits. 
These he places as between 1 part of the chloro-platinite in 
15 parts of water as a maximum strength, and 1 in 3000 as 
a minimum. Outside these limits in either direction there 
is a tendency to render the fine detail of the image of a 
yellowish colour. He also notes that no toning takes place 
unless the bath be in a distinctly acid condition. 


Clark alBo made experiments to determine the permanency 
of such prints. He points ont that the platinum and silver 
will form an alloy together which has not the stability of 
platinum, being, indeed, soluble in nitric acid. This process, 
therefore, is not so stable as the ordinary platinotype 
processes proper ; but, at the same time, the results of several 
tests with powerful oxidizing agents showed that its per- 
manency is superior to that of prints toned with gold in 
the ordinary way. 

Many variations of the above toning bath have been 
proposed from time to time, and, like gold toning, almost 
any combination may be used, providing the bath be acid. 
Mercier {Bull. Soc. Fran^,^ vi., 2, 194) recommends the 
following bath : — 

Chloro-platinite of potassium ... 1 to 2 parts. 

Phosphoric acid (pure) 5 „ 

Water 1000 „ 

Mercier gives also a formula for use with the ordinary 
platinic chloride of commerce, by means of which it is 
converted to the platinous stage, and the great loss in 
intensity in the image which always obtains when the 
ordinary chloride is used, is obviated : — 

Platinum chloride 2 parts. 

Neutral oxalate of potash "6 part. 

Water 100 parts. 

This solution is exposed to light until the colour changes 
to a ruby red and no precipitate is formed on the addition 
of a drop or two of a saturated solution of chloride of 


ammoniuin. The action is rapid in summer, but slow in 
winter. The bath is made up for use to a bulk of 1000 
parts by the addition of water. 

Burton (Photographic News) proposes another useful 
variation as follows : — 

Chloro-platinite of potassium ... 

... 2 grains. 

Citric acid 

Common salt ... 

n ,, 

Water up to 

... 1 ounce. 

It may be noted, generally, that the use of a mild organic 
acid is preferable to that of nitric acid where the surface of 
the print is in gelatine, as the latter acid has a tendency to 
cause stains on this medium. The addition of salt in Burton's 
formula is probably made in order to ensure the conversion 
of any free nitrate of silver on the print into the visible 
milky-white chloride. 

It follows that the last-mentioned bath may be used very 
advantageously with that class of papers that embraces both 
the developable and printing-out gelatino-chlorides and 
bromides of silver, or the following bath as originally given 
by Clark, and also by StiegUtz (Amateur Photographei% 
may be also successfully used : — 


Oxalate of potash neutral ... 

.. 5 ounces. 

Mono-potassic orthophosphate 

... 3 „ 

Water up to 

... 50 „ 


Chloro-platinite of potassium 

... 60 grains. 

Water up to 

... 2 ounces. 

* D is the same as the ordinary D solution of the Platinotype 




The toning bath congists of 3 parts of either of the 
D solutions, 1 part of P, and 2 parts of water. All the 
operations in connection with these papers are the same as 
those already described. 

Toning with other Metals of the Platinum Group. 

We except gold from this category, as its use is so well 
known in photography, but a few notes on the results 
obtainable by the rarer of the noble metals may be useful. 

Palladium, — Clark {Camera Gluh Journal^ vol. iv. p. 202) 
used a chloro-palladite of potassium for toning ordinary 
silver citrate and chloride prints, the strength of the solution 
being the same as when platinum was used. He notes that 
it tends to give images of a somewhat greeny-brown colour. 
Prints toned with palladium and afterwards intensified with 
silver gave very pure sepia tones. 

Indium, — Mercier {anU^ p. 138) gives the following bath 
for iridium toning, by which the results obtained are of a 
violet colour : — 

Tartrate of sodium 0*15 part. 

Double chloride of iridium and sodium 1*5 „ 
Water ... .. ;.. ... ... 1000 parts. 

The above bath is boiled, and 400 parts of water and 10 
parts of acetic acid are added ; when cold it is ready for use. 

Company, and, if preferred, their ordinary oxalate bath may be nsed 
instead, that is : — 

D * . Oxalate of potash neutral 8 ounces. 

Water up to 50 „ 


Osmium. — Mercier gives the following bath : — 

Yellow chloride of osmium (Fr6my's) 
amoniacal ... ••• ... ... 1 part. 

Chlorate of sodium '04 „ 

Succinate of sodium 4 parts. 

Water 1000 „ 

The prints change first to a burnt sienna colour, and, if 
toning be continued, to a bright blue, which does not appear 
to alter in the subsequent fixing bath. Mercier also notes 
that if mineral acids be added to this toning bath, the 
resulting colour is a violet, but in this case it is advisable 
to add sulphite of soda to the fixing bath. 

BJwdium. — Mercier notes some experiments with this 
salt, but states that in no case was he successful. 

It may be noted, generally, that prints that have been 
toned with iridium or osmium are capable of being toned 
again with gold, so that a further variety of coloura is 



The platinum process has, as a rule, been devoted to the 
production of prints by contact, but some years ago, in 
America, and also at the present time, enlargements have 
been made direct on the paper by means of the electric 
light. In a paper read before the Camera Club, one of 
us showed examples of enlargements made by himself, with 
an arc electric light of about 1100 candle power. This 
electric light is of but small power compared with that 
which can be obtained, as it consumed only about 1100 
watts of electricity. The apparatus required for this light 
is very limited, where the enlargement required is not 
more than nine times the area, and every photographer who 
has a direct current of electricity at his command, is in 
a position to avail himself of it. It is proposed in this 
chapter to describe the apparatus and the methods of 
adjustment when using the electric light of this dimension, 
and also with solar light. 

We win suppose that we are limiting ourselves to the 
enlargement of a quarter-plate of twice linear. 

In the first place we must have two condensers, preferably 


plano-convex, sufficient in diameter for our purpose, and 
it is convenient that they should be about nine inches focal 
length each. They can be obtained very cheaply, of cast 
glass, and there is no great precaution necessary to take 
in selecting them, beyond seeing that they are fairly free 
from bubbles ; if many bubbles are present the print is 
apt t3 show images of them, though, by keeping the negative 
a little way from the lens, they can be made to disappear. 
We can find the necessary diameter of the condensers by 
taking the length of the diagonal of the quarter-plate to 
the diameter of the condenser. It is a little over five inches, 
but it is convenient to allow an extra inch, which will 
make them six inches in diameter. This allows the negative 
to be in the cone of rays even when some distance from 
either one of them, a very necessary point, as we shall 
see when focussing. A convenient way of setting up the 
apparatus is as follows : — The condensers are mounted in 
two firm wooden-framed stands, with a device enabling 
their heights to be altered at pleasure. Their centres are 
so adjusted that they are of the same height above the 
table, on which they are used, as the lens used to enlarge 
with, and the height of the electric light is similarly 
adjusted (Fig. 4). One of the condensers, Ca, is placed in 
front of the electric light, E, with its plane side towards 
it in such a position that its axis passes through the electric 
arc. The distance of this lens is guided by its focal length. 
The arc should be placed just within its focal distance, 
so that it throws a circle of light, a little bit larger than 
the diameter of the lens, on a screen placed about twelve 
inches from it* In this disc of light the second condenser, 


C„ is placed, and it ehoold throw a cone of rays coming 
to an approximate focna of about seven inches from it. 
In this case the plane side of the condenser is aws; from 
the l^ht. A photographic lens of some eeven and a half 
inches focus, and which has a fairly flat field, is then, 
withont any stop being inserted, held in a perfectly rigid 
camera front, or in a clamp, and so placed that the 
focos of the rays, coming from the condenser, falls within 
its front combination. The negative, K, to be enlai^ed ia 
then inserted in a proper holder in front of the second 
condenser in such a manner that the image, when sharp, 

Fis. 4. 
is of the required size on a board, 8, to which a sheet of 
white paper has been pinned. It frequently happens that 
a circle of orange and blue light is seen cutting the picture, 
this shows that the adjustments are not accurate. If the 
coloured circle cuts the comers of the picture uniformly, 
it must be got rid of by moving the lens backwards till 
a clear circular white disc of the necessary size is obtained, 
and the negative most be moved backwards or forwards 
from the condenser, till a sharp image is again secnied. 
Patches of blue are due to the light from the arc in contra- 


distinction to that of the poles. The positive pole of the 
electric light should be the top pole, and be thrown a little 
behind the bottom or negative pole, and the cnrrent should 
be sufficiently strong to allow the white-hot crater of the 
positive pole to be clear of the latter, for it is this crater 
which creates the most photographically active light. When 
patches of blue light are seen they indicate that this position 
of the crater has not been secured. That the most 
photographically active light proceeds from the crater is 
easily proved by throwing an image of the poles on a 
piece of chloride paper by means of a lens, when it will be 
found that the image of the crater blackens the paper 
much more rapidly than that of any other portion of the 
luminous image. 

When the focus of the image is correct, platinum paper is 
placed on the focussing paper, and the exposure is given. 
With an electric light of about 1100 candles, the time for 
exposure for a thinnish negative will be from about 15 to 25 
minutes. With a denser negative it will, of course, be 
longer ; but it rarely happens that any negative will take more 
than an hour to print. For the purposes of enlargement 
the deepest shadows of the negative should be as nearly bare 
glass as possible, and any yellowness should be avoided. It 
should be remarked that the density of the negative, to give 
a good enlargement, may be less than that required for a 
contact print ; in fact, a rather feeble negative, if very 
bright, will give the best results. It is a good precaution 
to place a sheet of glass between the electric light and Cg. 

When sunlight is used, very much the same procedure is 
carried out ; but the condenser Cs, next the electric light, need 


not always be used, if the photographic lens employed is 
exactly the proper focus. A large looking-glass, M, is em. 
ployed to reflect the light on to the condenser next to the 
lens, and care is taken that the focns of the beam of the 
condenser falls within the lens ; so long as it does not travel 
ontside, it doee not matter if it is not always qnite central. 
Supposing the lens to he of slightly too long or too short a 
focal lei^th for the image (Fig. 5) of the necessary size, 
the focus of the condenser lying either too near or too far 
from the phot(^iapliic lens, L, to give a proper iUnniination 
of the field where the iu» is correct, then the oae of the 
second condenser, Ci, becomes necessary. In Fig. & it will 

be seen that the position of F„ the focus of Cg, can be cansed 
to recede or approach C,. The further F, is from it, the 
shorter will be the focns of 0„ and the closer it is (of conrse, 
within limits), the longer will be the focus. Hence C, is 
placed at such a distance from the condenser (behind which 
is the negative, N), the focus of the latter being altered 
to the necessary extent, that it falls exactly on the photo- 
graphic objective. The great point to observe is that the 
centres of the condensers be on the same axis. To secure 


this the objective is removed, and the mirror turned so that 
light coming through the aperture cut for the lens, occupies 
the centre of the focussing screen. The first lens is then 
approximately focussed, the small patch of light formed 
being also in the centre of the screen. The second con- 
denser is then placed in position to give the same result, 
after which the photographic objective is replaced. The 
negative is then put in position, the image f ocussed to the 
proper size, and the back condenser moved parallel to its 
position till a uniformly lighted field is secured. 

The printing with a bright sun is quicker than with the 
electric light, and a good print may often be obtained in ten 
minutes, or even less. This will be understood when it is 
considered that the light which falls on the negative is 
simply spread out to fall on the area of the enlargement. 
There is no loss of light by reflection and absorption, and it 
may be concluded that the exposure is about three times 
that which calculation would give. Suppose a negative has 
to be enlarged twice linear, and that a contact print can be 
obtained in one minute, then it will take twelve minutes to 
make the enlargement. There is nothing peculiar in manipu- 
lating the paper ; the great point is that it should be flat, 
and it is well to leave it ten minutes lying on a table in the 
room where the enlargement is to be made, before pinning 
it in position, so that it may possess the same moisture as 
the air in which it has to be exposed. Arrangements should 
be made to prevent diffused light reaching it during ex- 
posure, and yery obvious precautions should be taken to 
effect this. The prints produced are, as a rule, more even 
than the contact prints, for the margins of the print receive 



slightly leas expofiure than the centres, and, as of necessity, 
the margins of a negative are slightly less dense than its 
centre, on account of the want of perfectly eqoal illomi- 
nation of the field, a compensation is made in the camera 

A small calculation will show the relative values of the 
printing powers of sunlight and the electric light. Sunlight 
has the same value, optically, as 5000 candles when placed 
one foot off the screen. The electric light used has the value 
of 1100 candles. Hence, the value of sunlight is about 4i 
times that of the electric light, when placed one foot off. 
All we have to do is to compare the values of the two sources 
when falling on the condenser, which is next the photographic 
lens. If the light be six inches from the first condenser, 
evidently four times as much light will fall on it as would 
be the case if it were one foot off, but the area of the disc 
of light in which the second condenser is placed is at least 
eight inches in diameter. As the first condenser is six 
inches in diameter, the light on the second condenser is, 
therefore, only f| or -^ (say half) of that falling on the first. 
Had it aU fallen on it, it would have been equal to 4400 
candles, but owing to the increased disc, it is only equal to 
2200 candles, and as the photographically active rays in sun- 
light are about 1-3 times greater than that of the electric light, 
It foUows that the 2200 must be divided by 1-3, or the value 
of the hght formed. The intensity of the electric light com- 
pared with that of the sun is as 1700 to 5000, that is, the 
latter will pnnt three times more quickly than thTf« 
always supposmg the sunlight is that nea; midday and^m 
an unclouded sun with a dark sky. It may beX'tiT^ 


note the fact that the different thicknesses of glass cat off 
approximately the same amomit of the photographically 
active rays. Roughly, it may be said that f of these rays 
reach the plate, the different amounts of surface reflection 
due to the varying curvature of the glass, probably making 
up for the different absorptions. 





It is a matter of practical interest to know the rays of light 
to which platinotype is sensitive, since the relative rapidities 
of printing in winter and summer are in question. It must 
be recollected that in the winter, owing to the low altitude 
of the sun above the horizon, the blue rays are very much 
diminished, owing to the scattering by the fine atmospheric 
particles which intervene between it and the paper. It is, 
therefore, a point in favour of any printing process that it 
should be as sensitive as possible to the green rays, and, if 
possible, to the yellow and red rays. It has been said that 
the blue rays are diminished in winter, but a little more 
explanation, perhaps, may be required to make the matter 
plainer, for the same applies not only to winter printing, but 
to printing carried out at different times of the day. Sup- 
posing the different component and coloured rays of the 
light of the sun were unity when it was outside our atmos- 
phere, then the following would be the reduction of the 
different rays when the sun gradually approached the 
horizon : — 






Sun being above the horizon. 





19° 30' 


4 5 

•693 -632 
•669 ^494 
•427 ^334 
•296 -219 
•137 ^084 
•071 -033 



8° 30' 


7° 30' 


Just at 

Red (C) ... 
OrangefD) ... 
Green (E) ... 
Bine (F) ... 
Violet (G) ... 
Irimit of Violet 


This table shows that the violet light decreases enormously 
as the sun travels towards the horizon.. 

When platinum paper is exposed to the sunlight-spectrum, 
it is found that the maximum sensitiveness is close to Gr. In 
Fig. 5 are the results of a careful measure of a print taken by 
exposing platinotype paper to the spectrum. The sunlight 
was in a bright June day near noon. It will be seen that 
the paper is sensitive almost into the orange. Now, ordinary 
chloride of silver, as found in albumenized paper, is very 
much less so, and has its maximum of sensitiveness nearer 
the line H, or the boundary point between the ultra-violet 
and the violet. We may for our purposes take the maximum 
of the one at G, and of the other at H, as the position that 
governs the comparative sensitiveness of the two at different 
altitudes of the sun. If we compare the sensitiveness of 
the two at 30° and 14° 30' above the horizon, we shall see 
that, whilst the loss for platinotype would be only from '367 
to '137, or from 1 to '37, the loss for chloride would be 
from '254 to "071, or from 1 to 27. From this fact we have 
a good example of the increased general sensitiveness of the 


*>-!»«= „e3it I!"'"' to ^ "^ 


gradation given by platinotype in comparison with silver 
prints. The annexed diagram illoBtrates the difference 
between the two. The intensitira of the light acting in the 
two cases were the same, and varied from 1 to 3^ parte. It 
will be noticed that platinotype was practically black when 
only \ of the whole exposnre had been given, and was white 
at T^s ; whilst the toned silver print was only black when 
the full esposnre bad been given, and was practically white 




Fig. 7.— latenaities of ligbt-acting. 

when -^ had been given. The straight sloping lines show 
the general gradation of the two, and it does not differ much 
in either aa indicated by the angle of the slope of these 
lines. It appears from this diagram, that with a plucky 
negative, platinotype wonld give the best result, but with 
a thin negative, on account of the greater gradation in the 
parts of a print which are nearly white, the silver print 
would give the better print. The question of rapidity is 


also practically settled by these measnres, as far as these 
two specimens of platinnm and silvered paper are concerned. 
There is, however, a power of altering the gradation of 
prints in the preparation of the platinum paper, as Dr. Eder 
and Pizzighelli have shown. The addition of oxidizing 
agents to the iron salt produces a marked effect, as also does 
the heat the strength and temperature of the solution of 
oxalate used in development. 




It may be remembered that in Mr. Willis's specifications 
(p. 20) the use of other metals than platinum for the 
formation of a visible image is claimed, amongst which are 
palladium, iridium, and gold ; it is therefore necessary to 
examine the behaviour of these metals. 

As regards their use in the hot-bath process, Pizzighelli 
has experimented with them, and we have ourselves added 
to these results by undertaking a series of trials with these 
different metals, applied to paper prepared for the platinum 
in the bath process. 

In the hot process, palladium is substituted for platinum 
with complete success. From the great similarity of the 
chemical behaviour of these salts with those of silver and 
platinum, it was to be expected that it would do so, but 
its great expense hardly brings its use into the range of 
practicability. The resultant colour of photographs taken 
with palladious chloride is of a sepia-brown colour, but they 
are very subject to solarization — that is to say, the parts 
that have received the most exposure develop out lighter 
than the half-tones ; this phenomenon is also observable in 


platiimm printe, bnt in a less degree. Palladimn prints also 
possess the property of being capable of being toned by gold 
chloride, by which treatment they assome a violet coloor, 
and, at the same time, the effects of sokrization disappear. 

If the paUadions and platinons chlorides be mixed, the 
resnltant colour partakes of the nature of the combined 
salts being brownish black or blackish brown, as one or 
other of the salts prevails in its action. The brown colour 
that can be obtained by the use of palladium would no donbt 
be a useful ally in the hands of the artist, but the Platino- 
type Company prepare a special paper (sepia paper), by 
means of which the same results are obtainable. 

Iridium^ although also one of the platinum groups of 
metals, behaves differently from the others under the action of 
reducers. Although its compounds resemble in their action 
those of platinum, they have also considerable resemblance 
with those of iron, and Pizzighelli states distinctly that their 
use is not practicable, it being impossible to develop the 
iridium image by the same agents as would a platinum one. 

Oold. — ^The compounds of gold are, with the exception of 
the hyposulphite, all reducible by oxalate solutions when 
cold, and even the hyposulphite does not withstand the action 
of hot oxalate ; on this account gold also is not a feasible 
agent of which to form the positive image, as it could be 
reduced on the high lights as well as on the shadows. 

The Use op the above Salts in the Cold Process. 

In this process there is considerable difference in the 
chan ical action, as we have on the paper simply a metallic 


image, and we can therefore present to it the salt of any 
other metal simply in an aqueous solution. If platinum be 
so presented, we have seen that no action takes place ; but 
if gold in the form of an aqueous solution of the terchloride 
be applied, it is at once thrown down without the addition 
of any other substance as a developer. The colour assumed 
by the print is a purplish blue, almost a slate, but un- 
fortunately the result is marred by a very slight reduction 
of gold that also takes place over the high lights. The gold 
here is thrown down in the pinky state, and, to portraits, 
gives almost a natural colour to the high lights of the flesh. 

The above process is almost identical with the chrysotype 
process of Sir John Herschel, the only difference being in 
the salt of iron used to form the provisional image, the 
ferrous oxalate being substituted for the ammonio-citrate of 
iron of this worker. 

At the same time, we remarked that the gold is much 
more easily reduced than the platinum — ^that is to say, that 
less exposure is required. Thinking, therefore, that an 
addition of gold to the platinum might act as an accelerator, 
we tried a mixture of these two salts ; unfortunately the 
result was negative, as the two react mutually on each other, 
and a copious black precipitate is thrown down. 

Palladium in the form of the chloro-palladite of sodium 
acts well in the place of the platinum salt. Its behaviour 
is the same as in the hot-bath process. 



Hot Bath. Purthbe Formula. 

Lainer {Photograph%9che OorrespondenZy vol. xxx. p. 17) 
gives the following formula for preparing hot-bath paper. 
He OSes the following Bolutions. A. Normal ferric-oxalate 
solution (see formula, p. 58, ante). B. Iron chlorate 
solution, prepared by adding 8 parts of a 1 in 20 solution 
of oxalate of potash to every 100 parts of the normal iron 
solution A. G. Platinum solution made up of 1 part of 
chloro-platinite of potassium dissolved in 6 parts of water. 

To suit negatives of different qualities the proportions are 
tabulated hereunder : — 





A. ... . > • 
j3 ... • • • 
\J • . . • •• 









3-6 to 2-6 






4 to 5-5 



Ganichot (see Bull. 8oc. Fram^ise de Photographie^ vol. 
viii., N.S., p. 458) gives a formula for the preparation of 
platinum paper with the sodio instead of the potassio salt 
of platinum, which he claims not to suffer from damp. He 
prepares the following solutions : — 

A. Anhydrous iron perchloride ... 125 grams. 
Water 1000 

The solution is filtered, and ammonia added drop by 
drop, until no further precipitate is formed* The precipi- 
tate is a hydrated peroxide of iron. This is filtered and 



B. Oxalic acid 50 grams. 


This solution is boiled, and A solution in its moist state 
is added. The resultant is filtered and 2*50 grams of 
chloro-platinite of sodium is added, and the solution made 
up to 250 with water. Sized paper is coated with this 
solution and rapidly dried. It is printed from in the usual 
way, and developed on the following bath at ordinary 

Oxalic acid ... ... ... ... 28 grams. 

Chloro-platinite of sodium 2*5 „ 

Water ... ... ... ... ... 250 ccm. 

This process, it may be noted, partakes of the character of 
the hot-bath, cold-bath, and printing-out processes. 

Advanced Development of the Hot-bath Process. 

In a preceding chapter we have dwelt very fully on the 
ordinary manipulations to be carried out in working the 
hot-bath process in what may be called the ordinary way, 
but, as in other processes, there are special treatments 
which can be adopted for certain cases, constituting what 
one may call the higher possibilities of the process. Great 
latitude in treatment is undoubtedly to be met with in the 
ordinary hot-bath process, and this is more the case with 
the present brands of paper than with the older ones. We 
have, therefore, thought it advisable to resume, under the 
present heading, an account of what may almost be termed 
" tricks " that can be* played with this brand of paper. 


In the first case, in regard to keeping the paper dry. 
This is certainly a most wise and necessary provision, bnt 
still, by an intentional damping, certain efiFects may be 
produced even with the ordinary hot paper. For instance, 
damping hot-bath paper, preferably after exposure, affects 
its qualities in two ways. It lengthens the scale of the 
paper, and makes it, therefore, more suitable for printing 
from dense negatives, and it also warms the colour, making 
it a brown- instead of a blue-black. 

In order to get the fullest effects out of paper so damped, 
it will be advisable to work the developing solution at a 
temperature not higher than about 90^ F., to use the 
D salts instead of the plain oxalate, and, further, to strongly 
acidify the bath with oxalic acid. If warm tones are 
desired as well as a lengthened scale, a diluted oxalate bath 
can be used instead of the D salts, as these latter, at least 
in normal prints, have a tendency to keep the colour of 
the print cold. In the event of the oxalate being used, it 
should be diluted, potassium chloride added, and the proof 
be fully, and, indeed, over-printed. The following would be 
an approximation of a suitable bath : Two parts normal 
oxalate solution, two parts water, one part oxalic acid, and 
one-twentieth part potassium chloride. Development will 
be slow and under control. It may also be noted that paper 
that has been kept is more amenable to this treatment than 
new paper. 

If the D salts are used, they should be of normal strength 
(J pound of the mixed salts in 60 ounces of water), and 
not be acidified. Generally speaking, the D salts will 
always give a slower development than the oxalate, and. 


therefore, dilation is not so necessary to get development 
under control. 

To get flat prints, that is, those having bat few grada- 
tions, if oxalate is used the solation shoald be strongly 
acidified with oxalic acid. The acid may be added almost 
until the bioxalate begins to be precipitated. This develop- 
ment will give an image in which the haK-tones and 
shadows are weak, if the paper be dry. If the D salts are 
used, they shoald be acidified, and of normal strength. 
This is probably a better developer for weak negatives than 
the last, as the shadows are not weakened in intensity, but 
only the scale is shortened. Although we give these 
methods of dealing with weak negatives with a cold de- 
velopment, which are due to Mr. Willis's experiments, still 
we are of the opinion that the hot development is the best 
in this case, but it is interesting to notice the action under 
aU circumstances. We may also sum up the characteristics 
of the D salts when used for ordinary hot-bath paper, but 
at a low temperature, so as to be under control, for which 
we are indebted to the researches of Mr. Willis. 

The D salts tend to lengthen the time of development ; 
they tend to destroy granularity ; they tend to give less 
strength in the middle tones, if they are diluted ; they tend 
to give a weaker image all over, if acidified and concen- 
trated ; but when acidified and diluted slightly they only 
shorten the scale. 

In treating of the higher development of the sepia paper, 
it is very difficult to lay down fixed 'rules. As Mr. Willis 
himself admits, it is a very uncertain paper as regards its 
colom*, at least, and two batches are rarely alike. Quite 


lately, however, this paper has certainly been improved 
considerably, and the colour given by it is mnch nearer 
a tme sepia all through the scale, and not one colour in 
the half-tones and another in the shadows, as the former 
paper was apt to be. Captain Abney, at the request of 
Mr. Willis, has carefully measured the true colour of this 
later paper, and finds that it is very nearly a true sepia 
all through the scale, and is, indeed, a nearer approach 
to homogeneity even than a sepia-washed paper produced 
by the ordinary water-colour sepia (see Camera Club Journal^ 
vol. vii. p. 178). 

Generally speaking, the hotter the temperature of the 
developer, and the more it is acidified, the hotter will be 
the colour of the resulting print. A good bath is the 
normal oxalate, well diluted and acidified, and worked at 
150° F. Damp paper — and this sepia paper appears less 
susceptible to injury by moisture than the ordinary paper 
— is more suitable for dense negatives, and, per contra, dry- 
paper should be used for thin, negatives. We have not 
ourselves noticed that damp makes any difference to the 
colour of sepia paper, but cannot speak very certainly on 
this point. 

We must ask our readers not to look out for what may 
seem contradictions between these closing remarks and 
the directions given in the earlier portion of this work. 
The latter, like those issued by the Company, are plain- 
sailing directions, and should be followed out in all ordinary 
cases. But there mdy happen special conditions, such as 
unsuitable negatives, damp paper, special effects required, 
etc., and in such cases it is well to have some indication 


of the course to follow. Bat it must be remembered that 
in all the formulae given, or rather indicated, above, the 
utmost possible that can be done with the paper is meant, 
and every advanced worker must be prepared to vary these 
formulas if he finds that he is just overstepping the line 
that divides possibility from impossibility. Platinum paper 
has varied considerably since its first appearance in practical 
use, and still continues to vary, and the brands of paper 
•now sold are entirely different in their characteristics and 
behaviour from the earlier ones. The first paper sold 
required hard negatives, with strong contrasts ; it had to 
be kept scrupulously dry, and the temperature of develop- 
ment had to be kept very high indeed. The present paper 
can be normally worked with negatives that, if not thin, 
•are at least delicate ; in some cases moisture actually 
improves it, and it can be developed on almost a cold 
solution. Much of this is undoubtedly due to our superior 
knowledge in manipulating the paper, but still a great deal 
is due to the paper itself, and although we still strongly 
recommend the beginner to keep to the rigid rules laid 
down, there is nothing to prevent him when he becomes 
more advanced in getting the greatest expression possible 
out of the materials before him. 

Preparation of the Chloro-Platinite op Potassium. 

Although this salt can now be obtained from most of the 
photographic dealers, still occasions may arise when the 
worker may want to prepare it himself, and we therefore 
give one or two of the simpler methods of producing the 


same. The foUowing is the method advocated by Messrs. 

Pizzighelli and Httbl :— 

Take 50 grams of the ordinary chloride of platinum and 
dissolve in 100 c.c. of water, and filter if necessary. Heat 
this solution to 100^ 0. in a water-bath, and pass through it 
a stream of washed sulphurous acid gas. The yeUow Uquid 
will commence to turn red, a sign that the platinous salt is 
being formed. Test the solution from time to time with 
ammonium chloride. As long as any of the platinic salt 
remauis unconverted, an insoluble precipitate of chloro- 
platinate of ammonium will be given. As the precipitate 
becomes slighter the stream of sulphurous acid gas should 
be diminished more and more, until it is completely stopped, 
when no further precipitate is formed. The point to be 
aimed at is to convert aU the platinic salt, but no more, as 
continued action of the gas will form sulphide of platinum. 
On the other hand, insufficient gas will still leave platinic 
salt in the solution, which will separate out as insoluble 
chloro-platinate when the solution is mixed with potassium 

When reduction is complete, the solution, after standing 
twenty-four hours to cool, is poured into a basin, and a hot 
solution of potassium chloride, of a strength of 28 grams to 
50 c.c. of water, is added, and stirred, when the chloro- 
platinite of potassium will separate out in the form of a 
crystalline powder. This is allowed to cool and stand for 
twenty-four hours, when the precipitate is collected, washed 
in wBter, and then alcohol until it loses its acid reaction. 

The powder is then spread out to dry in the dark, and is 
then m a pure state ready for use. By this process about 


74 to 75 per cent, of the double salt should be obtained 
from each 100 grams of platinic chloride — that is, about 93 
per cent, of the theoretical quantity. The mother-liquor is 
of no use except for residues. 

Commercial chloro-platinite of potassium should be com- 
pletely soluble in water in the proportions of 1 to 6, and 
should not give an acid reaction. As bought the salt some- 
times has the appearance of a ruby crystalline mass, and 
sometimes of a red brick-dust. The two varieties are the 
same, the difference in colour being only due to finer sub- 

Other Methods. 

Carey Lea has lately published, in the Ammcan Jowmal 
of SciencBy the following methods of obtaining this salt (see 
Photographic NewSy 1894, p. 826) : — 

First Method, — Potassium acid sulphite. Potassium 
platinic chloride is to be moderately heated with solution 
of the acid sulphite. Convenient proportions are : platinum 
salt 12 grams, acid Mlphite 9 grams,^ water 160 c.c. The 
mixture can be placed over a hot-water bath in a covered 
vessel and left to itself. The reduction takes about ten to 
twelve hours, and is known to be complete when the 
solution has a pure red colour free from yellow. The cover 
is then removed, and the liquid evaporated to the crystal- 
lizing point. 

If, as may happen, the red chloride and the other salts 
crystallize out together, it is best to redissolve them by 


heat in a small quantity of water satnrated with potassimn 
chloride. The red salt then crystallizes ont first. 

Second Method. — ^Alkaline hjpophosphites. By reason 
of its great reducing powers, a very smaU proportion of 
alkaline hypophosphite is capable of converting the yellow 
platinum salt to the red ; theoretically, one part of hypo- 
phosphite should reduce nine or ten parts of platinum salt. 

Place a weighed quantity of platinum salt in a flask 
with 30 C.C. of water for each gram of the salt, and a 
quantity of. potassium hypophosphite equal in weight to 
one-ninth of the platinum salt. The flask is to be placed 
in a water-bath, which is kept at 80® to 90** C. In con- 
sequence of the small proportion of hypophosphite the 
action is slow, requiring about ten or twenty hours for 
complete conversion. No attention during the time is 
required, and the advantages are that the solution becomes 
sufficiently concentrated to crystallize on cooUng, and that 
the very small quantity of foreign matter introduced renders 
it easy to obtain a pure product. 

At 100° 0., the reduction to red salt takes place in about 
fifteen minutes. This method is practicable, but requires 
great circumspection. If the boiling is continued a little 
too long, the solution suddenly turns brown ; the reduction 
has gone too far. 

If a quick reduction is desired, it is better to use an acid 
sulphite as a reducing agent, and the following method 
gives satisfactory results : — 

In a flask is placed 300 c.c. of water, 24 grams of 
potassium platinic chloride, 12 grams each of potassium 
acid sulphite and potassium chloride. (Sodium acid sulphite 


should not be used, as its introduction interferes with the 
crystallization ; not, indeed, with the first crop of crystals, 
but later.) These are made to boil rapidly together for 
twenty-five minutes, reckoned from the time when actual 
boiling begins. The solution is allowed to cool, filtered if 
necessary, and placed in a large flat-bottomed glass or 
porcelain vessel. In a day or two the red salt will com- 
mence to form large crystals. The addition of the potassium 
chloride causes the red salt to crystallize out first. 

Using up Platinum Residues. 

When (dd oxalate or D-salts developers get very yellow 
and spent, ferrous sulphate may be added to them and the 
mixture be heated. Platinum will then be thrown down 
in the metallic state, and can be collected on a filter. 
Spoilt prints and waste paper, trimmings, residues from 
coating mixtures, etc., are best treated by burning. The 
ashes are then stirred in a paste of three parts strong 
hydrochloric acid and one part nitric acid, and allowed to 
digest a few hours at a temperature of 50® to 70*^ C. Dilute 
with water, and filter out all the solids left. The solution 
left is then treated with ammonia, and insoluble chloro- 
platinate of ammonium separates out, which on heating is 
easily reduced to metallic platinum. It is well to digest 
the precipitate thus obtained in hot hydrochloric acid to 
make sure that all the iron is dissolved out. The metallic 
platinum obtained by these means can be converted into 
platinic chloride by dissolving in aqua regia, t.a. three parts 
strong hydrochloric to one part strong nitric acids. 


Aftee-obtbntion of Warm Tones on Platinum Paper. 

Another method of altering the colonr of platinotype 
prints has been qnite lately introduced by Mr. Packham, 
and described by him at the Boyal Photographic Society, 
on February 12, 1895 (see Photographic News^ 1895, p. 108). 
This gentleman treats finished prints with a decoction of 
catechu, cutch, or gambia, the effect of which is to stain 
the blacks of the image a warm brown, leaving the whites, 
however, entirely clear. The toning bath he recommends 
is made up as follows : Befined catechu (a compound of 
several different varieties of catechu) dissolved in water in 
the proportion of a quarter ounce of the former to five of 

the latter. This is boiled for four or five minutes, and an 


ounce of alcohol then added as a preservative. This forms 
the stock solution. For use, about thirty to forty minims 
are diluted with a pint of warm water. The bath is used 
hot, and kept hot during use, but can be used cold, when 
its action is much slower. When the prints have assumed 
the colour desired, the operation is complete, and all that 
is required is a rinse or two in pure water. Packham notes 
that catechu is rich in tannic acid, which combines with 
platinum black under certain conditions. The process is 
patented (October 27, 1894, No. 24,968 ; abstract in British 
Journal of Photography^ December 14, 1894, p. 798). It 
may be noted that there is a strong similarity between this 
process and that of Liesegang, which we described (p. 97, 
ant£). The latter uses pyro (equally rich in tannic acid) to 
get the required stain. He also states that the stain takes 


equally well with carbon prints. It would be interesting 
to observe whether Packham's process does the same. The 
process is, however, too recent for us at present to form any 
judgment about it, but according to reports the colours 
obtained are very rich, and as it is decidedly simple, it 
should prove a useful addition to the platinotype- worker's 





Acidity of platinum solution, 45 
Actinism, comparison of sunlight 

and electric arc, 148 
Arrowroot as a size, 53 

Baldus, platinum toning, 8 
Bichromate of ammonium, use of, 

in cold-bath process, 113 
Blanchard, platinum toning pro- 
cess, 9 
Bollman, uranium and platinum 

process, 15 
Briant, toning platinotypes, 93 
Burnett, researches of, 24 
Bunushing platinotypes, 83 
Burton, platinum toning formula, 

139 . 
— >, reviyification of old platino- 
type paper, 85 

Calcium tube, 71 

Carranza, platinum toning, 7 

Catechu, or cutch, use of, in stain- 
ing platinotypes, 167 

Cembrano, experiments in printing- 
out process, 133 

Chlorate of iron solution, pre- 
paration of, 60 

Chlorate of potash, action of, on 
sensitizer, 49 

Chloro-platinite of potassium, use 
of, by Dobereiner, 2 

Chloro-platinite, use of, by Willis, 


, preparation of, 163 

, use of, by Burnett, 24 

Chloro-platinite of silver, 4 

-, palladium, toning by, 140 

Clark, platinum toning, 135 
Coating paper for hot-bath process, 

Cold-bath process, action of 

coloured glasses on, 123 
, comparison of deyelopers for, 


, development of, 117 

, introduction of, 23 

, preparation of, 113 

, restrainers, use of, 122 

, working directions for, 115 

Development of hot-bath paper, 


— , variations in, 80 

— to obtain sepia tones, 92 

of cold-bath paper, 117 

, advanced, of the hot-bath 

process, 159 
of the platinum in the bath 

process, 104 
Dobereiner, use of chloro-platinite 

of potassium, 2 
Dolland, toning platinotypes with 

gold, 96 



Drying hot-bath paper, 68 

«< D " salts, composition of, 104 

Eder, experiments on salts of iron, 

Electric light, use of, for direct 

enlargements, 143 
Enamels, toning with platinum, 8 
Enlargements, time of exposure, 147 
Exposure of hot-bath paper, 74 

Failures, cause and remedy, hot- 
bath process, 84 

Ferric-oxalate, behaiiour of, 33 

— , preparation of, 68 

Fitz-Payne, treatment of platino- 
types with uranium, 94 

Fiidng hot-bath paper, 79 

Flatness, cause of, 86 

Fog, cause of, 84 

Ganichot, platinum process, 158 
Gehlen, ethereal solution of plati- 
num, use of, 2 
Gelatine as size, 58 
Glass, coloured, result of printiiig 

through, 123 
Glazing, pktinotypes, 83 
Glycerine, use of, 114, 121, 132 
Gold chloride, action of, on pla- 
tmum, 14, 157 

, toning platinotypes with, 96 

— , use of, instead of platinum, 

Gradation of platinotypes, 153 
Granularity, cause of, 87, 110 
Gwenthlian, platinum toning pro- 
cess, 8 

Haakmann, platinum toning pro- 
cess, 8 
Herschel, platinum and lime water, 2 

Herschel, chrysotype, 13 
Hot-bath process, after treatment 

of prints, 83 

, advanced development, 159 

, choice of paper for, 61 

, coating paper for, 64 

, development of, 77 

, drying paper, 68 

— , exposure of paper, 74 

, failures, cause and remedy, 84 

, fixing and washing, 79 

, intensification of prints, 93 

, negatives suitable for, 82 

, preparation of paper, 52, 138 

, of linen, bb 

— , of wood, bb 

, printing, 72 

, production of sepia tones, 89 

, rapidity of, 76 

, retouching and spotting 

proofs, 83 
-, rough, surface paper, treat- 

ment of, 98 
— , sensitizing solution, composi- 
tion of, 57 

— , specification of process, 20 
— , storage of paper, 71 

treatment for different types 

of negatives, 81 
-, variations in development, 80 

Hunt, experiments with platinum, 2 

, proto-oxalate of iron, use of, 


Intensification by platinum, 10 
Iridium, use of, byMercier, 140, 156 
Iron salts, action of spectrum on, 34 

, action on noble metals, 15 

-— », examination of, suitable for 

platinotypes, 28, 31 
Iron solution, normal, preparation 

of, 58 



Johansen, cUoride of platinum and 
baryta, 2 

Krone, uraniam and platinum, 16 

Lainer, formula for cold -bath 

paper, 113 
, formula for hot-bath paper, 

Liesegang, staining of platinotypes 

by pyrogallol, 97 
light, suitable for coating paper 

in, 67 
Linen, use of, as a support, 55 
Luynes, gold and platinum process, 


Maugham, platinum toning, 8 
Mercier, iridium toning, 140 

, osmium toning, 141 
— , platinum toning, 138 

, rhodium toning, 141 

Mercuric chloride, action of, in 

sensitizer, 89 
-— , developer, 90, 120 
Merget, platinum process, 16 
Monckhoven, platinum process, 17 

Negative, class of, suitable for 

platinotypes, 128, 136 
, variation in treatment for 

different kinds of, 81 
Niepce, use of ferric chloride, 12 

Osmium, toning by means of, 141 
Oxalate of potash used by Willis, 17 
. developer, composition of, 77 
Oxidizing substances, action of, 48 

Packham, staining platinotypes, 167 
Pad, for coating paper, 65 
Palladium, use of, in toning, 140 

Palladium, use of , in hot-bath, 155 

— -, use of, platinum in the bath 
process, 157 

Paper, choice of, 51 

, rough-surface, treatment of, 


— , sizing of, 53 

PizzigheUi, direct reduction of 
platinum by light, 4 

— , examination of developers, 43 

, examination of salts of iron, 


— t, examination of salts of plati- 
num, 38 

— — , formula for printing-out pro- 
cess, 130 

— •, printing-out process, details 
of, 125 

Platinum in the bath process, 104 

, developers for, examination 

of, 42 

■ bichloride, composition of, 9 
— — , manipulations, 137 

, negatives suitable for, 136 

, salts of, action of the, 38 

toning, 9, 26, 135, 138, 139 

Poitevin, iron and uranium process, 

Potassium nitrite, use of, as re- 
strainer, 122 
Poupat, platinum toning, 7 
Printing, hot-bath paper, 70 

, rapidity of hot-bath paper, 76 

Printing-out process, Cembrano's 
experiments, 133 

, preparation of paper for, 129 

V. Pizzighelli's formula for, 


, suitable negatives for, 128 

, theory of, 126 

, Wellington's experiments in, 









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